Group node fixes

[pythongosssss]

Fixes 3 issues:

1. Fix crash on unlinked grouped reroute
   group_unlinked_reroute.json - Disconnect image link between the two group nodes, click queue

   • Before: Crashes on queue
   • After: Shows missing input error

2. Fix converted widget inputs
   group_widget_inputs.json - Convert two KSamplers to a group node

   • Before: Various issues - links disconnected, value lost, fixing the links and queuing gets links incorrect (Return type mismatch between linked nodes)
   • After: Works

3. Add basic support for reroute inputs connected to converted widget inputs
   reroute_converted_input.json - Convert reroute + latent node to group

   • Before: Unsupported, would add a INT widget to the group that does nothing
   • After: Works for reroutes connected directly to inputs, not via chains. I didn't want to have to basically duplicate the walking reroute path and want to refactor that out in future.

[Simn]

I tested this and confirm that it now fails properly when there's a missing connection. There's no popup about failed validation (which makes this somewhat easy to miss), but that sometimes happens with "normal" nodes as well.

[pythongosssss]

You're not seeing this when clicking queue?

[Simn]

Ah, I think the issue is that the popup only pops up if all paths to all outputs are invalid. I tend to have random preview images in the middle, so if I break something beyond that it's not going to jump at me to complain. But that's unrelated to group nodes in particular.