Image Slice Utility discarding good sections

[Gankra]

in utils/image_slice/image_slice.sh there's a hack to detect if a generated tile is just a blank transparent one that can be discarded. This is good and desirable.

Unfortunately it also discards uniform black squares, leading to regions of the background being totally absent, and the infamous crazy rendering bugs because there's nothing to refresh those regions.

Ideally this script should be fixed to behave correctly, or we should just remove the feature altogether and accept that we'll be downloading a bunch of transparent squares that do nothing (gross).