Fix potential null value access in `WaveformGraph` async resampling logic
Fix potential null value access in `WaveformGraph` async resampling logic

smoogipooo/osu-framework,ppy/osu-framework,peppy/osu-framework,peppy/osu-framework,smoogipooo/osu-framework,ppy/osu-framework,peppy/osu-framework,ppy/osu-framework