Blender Git Loki

Fix T72236: UV Stretching Overlay

The ratio for area stretching was packed into an unsigned int, but could
contain negative numbers. This flipped the negative numbers to high
positive numbers and rendered the wrong color in the stretching overlay.

I can remember during {T63755} I had to flip the sign to get the
correct result, but couldn't find out why that was needed. Now I know.

Reviewed By: fclem, mano-wii

Differential Revision: https://developer.blender.org/D6440