Fix synchronous `GetChannels` path in `Waveform`
Fix synchronous `GetChannels` path in `Waveform`

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