model_config not found error when conversion is interrupted part way through

[ssube]

If a model is being converted and that conversion is interrupted, because of an error, keyboard interrupt, or disk space, it will leave an empty or mostly-empty model directory that shows up in the select menu, but produces an error if you try to use it.

When converting to a diffusers directory, the first thing created is the directory and the last thing created is the pretrained model_config.json file. The "has this model been converted" check uses the existence of the directory, but that does not guarantee that the model is loadable, which requires the config file.

Checking for both the directory and config file should fix this. If one or both do not exist, attempt to convert the model again.