core: Cleanup internals of next_track a bit
core: Cleanup internals of next_track a bit

adamcik/mopidy,tkem/mopidy,jmarsik/mopidy,bacontext/mopidy,jcass77/mopidy,kingosticks/mopidy,ali/mopidy,mokieyue/mopidy,kingosticks/mopidy,hkariti/mopidy,jmarsik/mopidy,SuperStarPL/mopidy,ali/mopidy,bencevans/mopidy,swak/mopidy,adamcik/mopidy,vrs01/mopidy,swak/mopidy,ZenithDK/mopidy,jodal/mopidy,quartz55/mopidy,rawdlite/mopidy,diandiankan/mopidy,quartz55/mopidy,dbrgn/mopidy,ali/mopidy,diandiankan/mopidy,tkem/mopidy,ZenithDK/mopidy,ZenithDK/mopidy,hkariti/mopidy,rawdlite/mopidy,quartz55/mopidy,pacificIT/mopidy,pacificIT/mopidy,ZenithDK/mopidy,dbrgn/mopidy,glogiotatidis/mopidy,rawdlite/mopidy,mokieyue/mopidy,mopidy/mopidy,jcass77/mopidy,dbrgn/mopidy,mokieyue/mopidy,vrs01/mopidy,ali/mopidy,glogiotatidis/mopidy,diandiankan/mopidy,adamcik/mopidy,jmarsik/mopidy,tkem/mopidy,jodal/mopidy,hkariti/mopidy,glogiotatidis/mopidy,bencevans/mopidy,jcass77/mopidy,tkem/mopidy,swak/mopidy,bencevans/mopidy,hkariti/mopidy,vrs01/mopidy,bacontext/mopidy,glogiotatidis/mopidy,jmarsik/mopidy,rawdlite/mopidy,bencevans/mopidy,quartz55/mopidy,SuperStarPL/mopidy,kingosticks/mopidy,dbrgn/mopidy,jodal/mopidy,SuperStarPL/mopidy,swak/mopidy,SuperStarPL/mopidy,bacontext/mopidy,pacificIT/mopidy,mopidy/mopidy,diandiankan/mopidy,mokieyue/mopidy,pacificIT/mopidy,vrs01/mopidy,mopidy/mopidy,bacontext/mopidy