Allow "Pre-fill" use at 0 strength

[Danamir]

Trying to see if the "inpaint with model" method can do a better job than Krita's "Smart Patch Tool".

This code simply allows the strength to be set at 0% (instead of min. 1%). If a region is selected, the generate button now acts as a direct call to ComfyUI InpaintWithModel node with MAT_Places512_G_fp16 as model.

The results are different than the patch tool, but not really better.

I think this PR can safely be ignored, but it was fun nonetheless. 😅 If anyone can find another use for it...

[Danamir]

PS : I think this code may have messed-up the custom menu display. Bah.