Fix nullref when changing display mode without any BeatmapSets added
Fix nullref when changing display mode without any BeatmapSets added

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