FMod - Flood fill fix

Yesterday's fix to the level-size-restriction-related crash is working; I received word from the tester today. He discovered a different bug, though. Flood filling in large areas causes Abiathar to vanish. This is actually a crash due to a stack overflow. The flooding is done recursively, so in large uniform areas the recursion can go too deep. This doesn't happen very often in normal levels, but it came up with Rise of the Triad because those levels are a fixed 128x128 (pretty large). So today, I rewrote that section to use a loop instead of recursive calls. That solved the problem.