Improve the error message when Hugging Face resource isn't found a the referenced location.

[meanderingstream]

If a users enters an incorrect hf: resource location, say GPT2 instead of gpt2, the error returned indicates a missing ETag. The error would be more useful if it indicated that the resource was not found at GPT2 or whatever the location the user entered.

[jonatanklosko]

FTR the reason why the error is confusing is that for "GPT2" instead of 404 HF returns 307 and redirects to "gpt2".