BE will crash when execute stream load, if bitmap field does not specify BITMAP_UNION type.

[godcat950081]

BE will crash when execute stream load, if bitmap field does not specify BITMAP_UNION type.

Steps to reproduce the behavior:

1. bitmap field does not specify BITMAP_UNION when create table.
   '''
   CREATE TABLE bitmaptable
   (
   TSID BIGINT NOT NULL,
   PKEY VARCHAR(96) NOT NULL,
   EDITFLAG BITMAP NULL
   )
   UNIQUE KEY(TSID,PKEY)
   DISTRIBUTED BY HASH(TSID) BUCKETS 10;
   '''

2. data file "111.txt" as the following:
   '''
   555;666;1,2,3
   777;888;1,2,3
   '''

3. exec stream load:
   '''
   curl --location-trusted -u user:pwd -H "column_separator:;" -H "columns:TSID,PKEY,tmp,EDITFLAG=bitmap_from_string(tmp)" -T /mydata/bitmap/111.txt -H "label:job1" http://172.17.0.2:8040/api/dolap/bitmaptable/_stream_load
   '''

4. BE will crash.