Fix 2 annoying crashes

Fixes FreeMipmapColormap crash that often happens in longer playsessions on servers with many different maps

also fixes some music changes which are set to fade the music volume that sometimes crash the game

Both are Backports from SRB2 and have recently been also merged into Galaxy fork

Credits for those go to Lactozilla from Sonic Team Jr.

I also include a map which i made specifically for testing the Music fade crash fadetest3.zip