Fix file pointer not initialized in rnnoise_model_from_buffer

[henkelmax]

This causes the null check in rnnoise_model_free to be not NULL when creating a model using rnnoise_model_from_buffer and thus trying to close a file handle that does not exist.

rnnoise/src/denoise.c

Lines 236 to 241 in 70f1d25

	RNNModel *model;
	model = malloc(sizeof(*model));
	model->blob = NULL;
	model->const_blob = ptr;
	model->blob_len = len;
	return model;

rnnoise/src/denoise.c

Line 272 in 70f1d25

if (model->file != NULL) fclose(model->file);

[orvitpng]

Patch looks good to me. On a related note: rnnoise_model_from_filename seems to have a similar issue, calling rnnoise_model_from_file without guarding against fopen failure. If f == NULL, fseek is UB. Do we really even need a *_from_filename in this API? I'd prefer if path resolution, error handling, etc is left to the caller.