Support loading Gemma3 QAT GGUF models
Author: Isotr0py
Pull request: yes

# What does this PR do?

originally reported in vllm: https://github.com/vllm-project/vllm/issues/14723#issuecomment-2817093067
- Gemma3 QAT GGUF checkpoint doesn't have `general.basename` field in metadata
- This PR handles this edge case to avoid `KeyError: 'general.name'` raising


## Before submitting
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- [ ] Did you write any new necessary tests?


## Who can review?

@SunMarc @MekkCyber

Anyone in the community is free to review the PR once the tests have passed. Feel free to tag
members/contributors who may be interested in your PR.

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