Avoid exceptions when Gemini responses are blocked

[tronikos]

Breaking change

Proposed change

For offensive queries the library sometimes throws BlockedPromptException or StopCandidateException which are already caught but other times it just returns empty parts which causes a ValueError when converted to text. Avoid that by responding with: "Sorry, I had a problem talking to Google Generative AI. Likely blocked"

(Ignore the dependency upgrade, that is being done in https://github.com/home-assistant/core/pull/116845)

Type of change

• [ ] Dependency upgrade
• [x] Bugfix (non-breaking change which fixes an issue)
• [ ] New integration (thank you!)
• [ ] New feature (which adds functionality to an existing integration)
• [ ] Deprecation (breaking change to happen in the future)
• [ ] Breaking change (fix/feature causing existing functionality to break)
• [ ] Code quality improvements to existing code or addition of tests

Additional information

• This PR fixes or closes issue: fixes #111617
• This PR is related to issue:
• Link to documentation pull request:

Checklist

• [ ] The code change is tested and works locally.
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