5.802: Assets with no `uncropped_edge` but with `rescaling_factor` can be smaller than the canvas in the thumbnail

[Wolfy76700]

When using UMVC3 base_files/icon assets v2.01 in the thumbnail generator, Venom and other characters with a smaller than 1 rescaling factor not only appear smaller than they should, but also do not respect the canvas constraint from the lack of uncropped edge