Pause music when volume is 0

Music was played in background even when volume was 0, this resulted in
30kb / s constant diskreads which can cause stutter if a platter-disk is already
under heavy load (torrents etc)
Merge branch 'bugfix/reducelag' of https://github.com/Crotalus/fa into bugfix/reducelag

Conflicts:
	lua/UserMusic.lua