More solid bug fixes

Attempts at fixing some clipping bugs, which uncovered more clipping bugs, which uncovered... let's just say I had a lot of fun. I also worked a bit on the semisolid platforms so that you can't glitch through them. The game should be more glitchproof now.

Any feedback is welcome, especially if you did manage to glitch through semisolids or walls in any way, same with the treasure chest.