Fix MusicController doing work in the background when not visible.
Fix MusicController doing work in the background when not visible.

default0/osu,EVAST9919/osu,smoogipoo/osu,DrabWeb/osu,NeoAdonis/osu,peppy/osu,Damnae/osu,NeoAdonis/osu,naoey/osu,DrabWeb/osu,smoogipoo/osu,osu-RP/osu-RP,ZLima12/osu,naoey/osu,ppy/osu,naoey/osu,theguii/osu,2yangk23/osu,ppy/osu,smoogipoo/osu,DrabWeb/osu,peppy/osu,NeoAdonis/osu,ppy/osu,peppy/osu-new,2yangk23/osu,UselessToucan/osu,nyaamara/osu,Nabile-Rahmani/osu,Frontear/osuKyzer,UselessToucan/osu,smoogipooo/osu,EVAST9919/osu,RedNesto/osu,johnneijzen/osu,tacchinotacchi/osu,Drezi126/osu,johnneijzen/osu,peppy/osu,NotKyon/lolisu,UselessToucan/osu,ZLima12/osu