Gracefully handle edge cases in harmony utils

[Ithanil]

Purpose

This PR adds better handling of the following situations in harmony_utils:

1. If input content has - for some reason - no text attribute, KeyError is avoided by using using .get() with empty string fallback.
2. Sometimes GPT-OSS models will emit commentary messages without recipient, leading to .startswith() being called on NoneType. This PR adds checks for None. In that case ultimately still a ValueError will be raised, but with a more accurate error message.

[gemini-code-assist]

Code Review

This pull request introduces graceful handling for two edge cases in harmony_utils.py. First, it prevents a KeyError by using .get() with a default value when parsing chat input content that may lack a 'text' attribute. Second, it avoids AttributeError when a message recipient is None by adding explicit None checks before calling string methods. The changes are correct, well-contained, and effectively improve the robustness of the code as described. I have no further suggestions.

[github-actions]

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[heheda12345]

LGTM! Thanks for the fix.