Window cutter doesn't handle joining between its two states well

[LemonInTheDark]

Ok so like the idea of the window cutter is to have 2 sets of bitmasked states, one for windows touching nothing/windows, and one for windows flush against a wall.

The idea is we need to fill that space as if we were smoothing, but only sometimes.

The trouble is we don't have joining sprites between the two, so where they meet we just get harsh cutoff