Fix hash aggregate edge case

[andyfengHKU]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 92.11%. Comparing base (293b4e6) to head (851cffe).

Files	Patch %	Lines
...cessor/operator/aggregate/aggregate_hash_table.cpp	50.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #3172   +/-   ##
=======================================
  Coverage   92.10%   92.11%           
=======================================
  Files        1170     1170           
  Lines       44188    44188           
=======================================
+ Hits        40698    40702    +4     
+ Misses       3490     3486    -4     

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