Fix finish_reason logic in Azure AI client streaming response

[张大侠 (litterzhang)]

Summary

This PR fixes a bug in the Azure AI client where the finish_reason logic for TOOL_CALLS was being processed after a potential None check, which could cause a mismatch when choice is None.

Changes

• Moved the finish_reason logic for TOOL_CALLS from lines 557-558 to be part of the choice processing block (after line 525)
• This ensures the finish_reason is properly set when choice exists and prevents potential mismatches

Bug Description

The original code had lines 557-558 checking \choice.finish_reason\ after line 554 where \inish_reason\ could be None and throw an exception. The logic should be moved to within the loop where \choice\ is guaranteed to exist, specifically after line 525 where \inish_reason\ is initially set.

Testing

• Code compiles without errors
• Unit tests pass (if applicable)

Fixes the finish_reason mismatch bug when choice can be None in streaming responses.

[张大侠 (litterzhang)]

Hi, could any contributors review this PR ? Without this change, I have to change the local code when using azure_ai_client.

[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 80.95%. Comparing base (c469fc0) to head (37df5e8).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...t/src/autogen_ext/models/azure/_azure_ai_client.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6963   +/-   ##
=======================================
  Coverage   80.95%   80.95%           
=======================================
  Files         237      237           
  Lines       18258    18258           
=======================================
  Hits        14780    14780           
  Misses       3478     3478           

Flag	Coverage Δ
unittests	80.95% <50.00%> (ø)

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