Refreshing with a missing loader changes the model to a default

Hey there,

I noticed that clicking the refresh button causes loaders (e.g. checkpoint loader) to revert to the first model in the folder if the previous model can no longer be found.

This seems intentional based on: https://github.com/comfyanonymous/ComfyUI/blob/7f4725f6b3f72dd8bdb60dae5dd2c3e943263bcf/web/scripts/app.js#L2208-L2209

I am wondering whether there is a reason that this is done rather than keeping the previous model, even if it no longer exists, as this would mean the prompt would fail validation when you run it due to the missing model, and it would require the user to fix it. This seems better than the current behaviour where it would silently change the model and run fine, but may not be what the user expects, as it has changed the model without the user's knowledge.