fix: prevent UnboundLocalError for choice variable in stream method

[tkasuz]

Description

The choice variable in the stream method could be unbound when accessing choice.finish_reason, causing an UnboundLocalError

Related Issues

Documentation PR

Type of Change

Bug fix

Testing

How have you tested the change? Verify that the changes do not break functionality or introduce warnings in consuming repositories: agents-docs, agents-tools, agents-cli

• I ran hatch run prepare

Checklist

• I have read the CONTRIBUTING document
• I have added any necessary tests that prove my fix is effective or my feature works
• I have updated the documentation accordingly
• I have added an appropriate example to the documentation to outline the feature, or no new docs are needed
• My changes generate no new warnings
• Any dependent changes have been merged and published

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[mkmeral]

Thanks for identifying the bug and opening up a PR. However, this was already fixed with #1099, so we can close out this one.