fix: index of choice in stream mode was always 0

[hustxiayang]

Description

Index of choice was always set as 0. In vertex api, it would return several parts in one chunk

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.96%. Comparing base (40fa3d6) to head (f347c33).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1487   +/-   ##
=======================================
  Coverage   83.95%   83.96%           
=======================================
  Files         143      143           
  Lines       12618    12618           
=======================================
+ Hits        10594    10595    +1     
+ Misses       1408     1406    -2     
- Partials      616      617    +1     

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[hustxiayang]

/retest

[hustxiayang]

/retest

[hustxiayang]

#1478

[nacx]

Could you please add unit tests so that we don't break this by mistake in the future?

[yuzisun]

will merge after adding the test

[hustxiayang]

@nacx Sure, would add it. Thanks a lot for the comment!