Fix import failures if single set has multiple conflicting OnlineBeatmapIDs
Fix import failures if single set has multiple conflicting OnlineBeatmapIDs

Resolves #2970.

ZLima12/osu,naoey/osu,DrabWeb/osu,NeoAdonis/osu,UselessToucan/osu,2yangk23/osu,ppy/osu,NeoAdonis/osu,johnneijzen/osu,peppy/osu,NeoAdonis/osu,smoogipoo/osu,2yangk23/osu,naoey/osu,ZLima12/osu,UselessToucan/osu,naoey/osu,peppy/osu,johnneijzen/osu,peppy/osu,EVAST9919/osu,smoogipooo/osu,EVAST9919/osu,DrabWeb/osu,ppy/osu,DrabWeb/osu,UselessToucan/osu,smoogipoo/osu,peppy/osu-new,ppy/osu,smoogipoo/osu