Fix visual test crash when BeatmapInfo doesn't have a BeatmapSet.
Fix visual test crash when BeatmapInfo doesn't have a BeatmapSet.

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