ggml : speed up model loading (#29598)

* ggml : speed up model loading

A crafted model could hang the server for a very long time, try with:

    llama-cli -hf angt/test-gguf-1Mkv -hff model.gguf

Signed-off-by: Adrien Gallouët <angt@huggingface.co>

* Avoid empty keys

Signed-off-by: Adrien Gallouët <angt@huggingface.co>

* Fix

Co-authored-by: Johannes Gäßler <johannesg@5d6.de>

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Signed-off-by: Adrien Gallouët <angt@huggingface.co>
Co-authored-by: Johannes Gäßler <johannesg@5d6.de>