Fix `BeatmapDifficultyCache` not working with detached beatmaps
Fix `BeatmapDifficultyCache` not working with detached beatmaps

peppy/osu,NeoAdonis/osu,peppy/osu,NeoAdonis/osu,ppy/osu,ppy/osu,peppy/osu,ppy/osu,NeoAdonis/osu