If float32 download option is selected, subsequent code fails

[lutusp]

I executed the download script "models/download_models.sh" with these arguments: "essential big-big float32". This doesn't download the "bf16" variants. This in turn causes the inference/text_to_image.ipynb script to fail, because it expects the "bf16" variants to be present and doesn't manage the exception.

Some users may want only one or the other variant of the weights, not both, but this may trigger an unmanaged exception.