Add missing None check for hf_quantizer (#28804)
* Add missing None check for hf_quantizer
* Add test, fix logic.
* make style
* Switch test model to Mistral
* Comment
* Update tests/test_modeling_utils.py
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Co-authored-by: Younes Belkada <49240599+younesbelkada@users.noreply.github.com>
