[r7277] 5tile high walls + pak192 overflow problem when zoomed in

[Leartin]

okay, this is a bit obscure and I'm not sure how often it would even happen in a normal game.

by placing a "steep slope" on top of a wall that is already three levels high, you can create a wall that is five level high. In pak 192, if you zoom in on such a wall, the upmost wall tiles will appear beneth the lowest point of the wall, leaving a hole of dirty pixels. Since this only happens in pak192.comic, not in pak128, I assume it's due to an overflow in the y-position, which probably only allows for 128 pixels.

[kierongreen]

Technically it shouldn't be allowed as the biggest wall height should be 4. However since it was easier to fix the overflow than prevent the few cases where you can build a 5 tile high wall I fixed the overflow. Try in 7278.