Fix gemma model conversion

[Galunid]

fixes #7964

Untested, since I cannot download gemma without going through license hoops.

@0wwafa Would you mind giving it a try?

[0wwafa]

hmm I solved that by commenting a line in gguf writer...
it seems that in gemma there are multiple chat-templates.
by commenting the line when it raises an exception when there is a duplicate key I cause the last one to overwrite the previous one.

alternatively, I could take the first one.
I don't understand your patch...

[0wwafa]

about the hoops: a single click on huggingface doesn't seem much of a hoop.

[bartowski1182]

@0wwafa there aren't 2 chat templates, it's just being set twice accidentally because 2 places do it, and Gemma happens to be the only one that's calling both of those places

[MoonRide303]

Gemma 2 models were just released on HF. Trying to convert gemma-2-9b-it results in:

INFO:hf-to-gguf:Loading model: gemma-2-9b-it
ERROR:hf-to-gguf:Model Gemma2ForCausalLM is not supported

[Galunid]

See #8156

[Galunid]

This is no longer a problem on master