The error result of decimal agg

[EmmyMiao87]

Describe the bug
The result of decimal agg is error when stream load.

To Reproduce
Steps to reproduce the behavior:

1. make a file with two column "1 123456789012345678.123456789" "1 123456789012345678.123456789"
2. create a table with a decimal column which is a sum agg column
   CREATE TABLE sum_decimal( tinyint_keytinyint(4) NOT NULL COMMENT "", decimal_most_value decimal(27, 9) SUM NOT NULL COMMENT "" ) ENGINE=OLAP AGGREGATE KEY(tinyint_key) DISTRIBUTED BY HASH(tinyint_key) BUCKETS 1 PROPERTIES ( "storage_type" = "COLUMN" );
3. insert file into table using stream load
4. show result of stream load
   +-------------+------------------------------+
   | tinyint_key | decimal_most_value |
   +-------------+------------------------------+
   | 1 | 246913578024691355.999999999 |
   +-------------+------------------------------+

Expected behavior
the result of load is following:
+-------------+------------------------------+
| tinyint_key | decimal_most_value |
+-------------+------------------------------+
| 1 | 246913578024691356.246913578 |
+-------------+------------------------------+

Screenshots
The old broker load and mini load have the correct result while stream load and new broker load have the incorrect result. So the problem must be happened in agg of olap engine instead of agg of dpp sink.

Additional context
Add any other context about the problem here.

[EmmyMiao87]

#1272