[Fix](fe) Fix NPE in OlapTableSink.createPaloNodesInfo due to concurrent drop backend

[bobhan1]

What problem does this PR solve?

Issue Number: close #xxx

Related PR: #xxx

Problem Summary:

Release note

None

Check List (For Author)

• Test

  • Regression test
  • Unit Test
  • Manual test (add detailed scripts or steps below)
  • No need to test or manual test. Explain why:
    • This is a refactor/code format and no logic has been changed.
    • Previous test can cover this change.
    • No code files have been changed.
    • Other reason

• Behavior changed:

  • No.
  • Yes.

• Does this need documentation?

  • No.
  • Yes.

Check List (For Reviewer who merge this PR)

• Confirm the release note
• Confirm test cases
• Confirm document
• Add branch pick label

[hello-stephen]

Thank you for your contribution to Apache Doris.
Don't know what should be done next? See How to process your PR.

Please clearly describe your PR:

1. What problem was fixed (it's best to include specific error reporting information). How it was fixed.
2. Which behaviors were modified. What was the previous behavior, what is it now, why was it modified, and what possible impacts might there be.
3. What features were added. Why was this function added?
4. Which code was refactored and why was this part of the code refactored?
5. Which functions were optimized and what is the difference before and after the optimization?

[bobhan1]

run buildall

[doris-robot]

TPC-H: Total hot run time: 34700 ms

machine: 'aliyun_ecs.c7a.8xlarge_32C64G'
scripts: https://github.com/apache/doris/tree/master/tools/tpch-tools
Tpch sf100 test result on commit 9e002ab86548f573879d379daab0f24e54497b30, data reload: false

------ Round 1 ----------------------------------
q1	17646	4147	4082	4082
q2	2064	364	228	228
q3	10122	1332	723	723
q4	10217	820	314	314
q5	7515	2156	1875	1875
q6	183	171	135	135
q7	1001	877	703	703
q8	9354	1415	1127	1127
q9	7095	5322	5315	5315
q10	6776	2401	1951	1951
q11	526	321	302	302
q12	661	721	598	598
q13	17771	3680	2998	2998
q14	298	299	267	267
q15	581	521	514	514
q16	664	666	624	624
q17	705	853	495	495
q18	7496	7019	7066	7019
q19	1107	980	599	599
q20	420	362	257	257
q21	4305	3943	3588	3588
q22	1077	1025	986	986
Total cold run time: 107584 ms
Total hot run time: 34700 ms

----- Round 2, with runtime_filter_mode=off -----
q1	4063	4061	4054	4054
q2	331	387	333	333
q3	2118	2634	2304	2304
q4	1340	1712	1286	1286
q5	4295	4373	4913	4373
q6	239	176	134	134
q7	2083	1979	1807	1807
q8	2679	2727	2565	2565
q9	7749	7719	7247	7247
q10	3113	3317	2839	2839
q11	592	514	504	504
q12	709	740	633	633
q13	3432	3876	3285	3285
q14	280	322	311	311
q15	557	533	516	516
q16	609	717	636	636
q17	1166	1409	1376	1376
q18	8168	7773	7537	7537
q19	857	840	887	840
q20	2058	2039	1934	1934
q21	5027	4646	4439	4439
q22	1081	1039	1009	1009
Total cold run time: 52546 ms
Total hot run time: 49962 ms

[doris-robot]

TPC-DS: Total hot run time: 178619 ms

machine: 'aliyun_ecs.c7a.8xlarge_32C64G'
scripts: https://github.com/apache/doris/tree/master/tools/tpcds-tools
TPC-DS sf100 test result on commit 9e002ab86548f573879d379daab0f24e54497b30, data reload: false

query5	5335	614	485	485
query6	331	223	201	201
query7	4205	458	281	281
query8	299	239	230	230
query9	8758	2561	2546	2546
query10	555	351	321	321
query11	15257	15038	14617	14617
query12	180	115	115	115
query13	1279	521	409	409
query14	6325	3277	2968	2968
query14_1	2869	2899	2862	2862
query15	215	201	181	181
query16	895	475	382	382
query17	1140	716	613	613
query18	2712	464	340	340
query19	228	224	197	197
query20	123	117	107	107
query21	220	137	113	113
query22	3972	4030	3805	3805
query23	16567	16427	16029	16029
query23_1	16169	16127	16023	16023
query24	7427	1661	1243	1243
query24_1	1264	1244	1236	1236
query25	557	481	424	424
query26	1242	264	157	157
query27	2750	466	297	297
query28	4466	2161	2142	2142
query29	790	549	430	430
query30	310	245	219	219
query31	855	685	639	639
query32	76	70	68	68
query33	531	331	279	279
query34	910	906	556	556
query35	782	847	718	718
query36	863	906	813	813
query37	132	88	76	76
query38	2845	2868	2819	2819
query39	829	753	710	710
query39_1	699	690	713	690
query40	225	138	120	120
query41	66	64	63	63
query42	106	104	103	103
query43	429	427	412	412
query44	1324	755	753	753
query45	199	188	179	179
query46	875	972	610	610
query47	1700	1737	1626	1626
query48	315	325	260	260
query49	626	426	348	348
query50	662	297	218	218
query51	3896	3836	3849	3836
query52	101	109	103	103
query53	324	352	297	297
query54	297	262	245	245
query55	74	75	70	70
query56	297	300	314	300
query57	1155	1148	1075	1075
query58	273	252	252	252
query59	2392	2445	2419	2419
query60	304	311	287	287
query61	162	151	152	151
query62	711	671	609	609
query63	328	297	296	296
query64	4902	1281	1010	1010
query65	4007	3958	3995	3958
query66	1385	440	321	321
query67	15140	15181	14950	14950
query68	2691	1032	762	762
query69	440	348	317	317
query70	1082	1002	1000	1000
query71	332	308	287	287
query72	6330	5214	5289	5214
query73	540	620	314	314
query74	8849	8934	8665	8665
query75	3090	3143	2776	2776
query76	2894	1140	741	741
query77	348	398	297	297
query78	9471	9695	8875	8875
query79	1458	875	599	599
query80	1226	652	551	551
query81	555	267	238	238
query82	405	136	105	105
query83	372	252	238	238
query84	251	117	93	93
query85	974	508	460	460
query86	400	300	289	289
query87	3057	3099	2941	2941
query88	3306	2257	2256	2256
query89	458	425	386	386
query90	1992	157	153	153
query91	174	169	146	146
query92	74	69	64	64
query93	1102	915	559	559
query94	536	306	260	260
query95	567	336	306	306
query96	590	450	205	205
query97	2233	2289	2228	2228
query98	206	196	192	192
query99	1302	1314	1217	1217
Total cold run time: 254497 ms
Total hot run time: 178619 ms

[doris-robot]

ClickBench: Total hot run time: 27.39 s

machine: 'aliyun_ecs.c7a.8xlarge_32C64G'
scripts: https://github.com/apache/doris/tree/master/tools/clickbench-tools
ClickBench test result on commit 9e002ab86548f573879d379daab0f24e54497b30, data reload: false

query1	0.06	0.05	0.04
query2	0.10	0.05	0.04
query3	0.25	0.08	0.09
query4	1.61	0.12	0.11
query5	0.30	0.26	0.27
query6	1.16	0.64	0.63
query7	0.03	0.02	0.02
query8	0.05	0.04	0.04
query9	0.58	0.51	0.50
query10	0.56	0.56	0.56
query11	0.16	0.11	0.10
query12	0.14	0.12	0.11
query13	0.62	0.60	0.60
query14	1.00	1.00	0.99
query15	0.81	0.79	0.81
query16	0.41	0.43	0.39
query17	0.95	1.05	1.04
query18	0.24	0.21	0.22
query19	1.92	1.83	1.84
query20	0.02	0.01	0.01
query21	15.46	0.28	0.15
query22	4.76	0.05	0.04
query23	16.00	0.28	0.10
query24	1.19	0.29	0.58
query25	0.11	0.06	0.06
query26	0.14	0.14	0.14
query27	0.09	0.05	0.05
query28	3.98	1.21	1.02
query29	12.62	4.00	3.27
query30	0.29	0.13	0.12
query31	2.81	0.62	0.39
query32	3.25	0.56	0.46
query33	3.03	3.04	3.02
query34	16.76	5.16	4.52
query35	4.63	4.56	4.57
query36	0.66	0.49	0.49
query37	0.11	0.07	0.07
query38	0.07	0.04	0.04
query39	0.04	0.03	0.03
query40	0.17	0.15	0.13
query41	0.09	0.03	0.03
query42	0.04	0.03	0.03
query43	0.04	0.03	0.04
Total cold run time: 97.31 s
Total hot run time: 27.39 s

[bobhan1]

run cloud_p0

[bobhan1]

run external

[hello-stephen]

FE Regression Coverage Report

Increment line coverage 0.00% (0/2) 🎉
Increment coverage report
Complete coverage report

[liaoxin01]

LGTM

[dataroaring]

LGTM

[github-actions]

PR approved by at least one committer and no changes requested.

[github-actions]

PR approved by anyone and no changes requested.