When custom audio renderers are added, app would crash if not removed before disconnecting

[davidzhao]

This relates to the use of custom audio renderers:

    nonisolated
    func participant(_ participant: RemoteParticipant, didSubscribeTrack publication: RemoteTrackPublication) {
        if let audioTrack = publication.track as? RemoteAudioTrack {
            audioTrack.add(audioRenderer: audioRenderer)
        }
    }

When this is added and the session is disconnected, this would crash fairly frequently.

[dfed]

I'm able to work around this in the majority case by removing the custom renderer before disconnect happens, but sometimes there's a race I can't avoid and we end up crashing. This is quickly becoming one of our top crashers. Crash is easy to reproduce in the simple case at least. Let me know if I can provide more info here.

[hiroshihorie]

I have a fix here, but it needs more testing. Also it will expose AVAudioPCMBuffer instead of CMSampleBuffer. If you still need CMSampleBuffer I might write a helper func in the SDK.
webrtc-sdk/webrtc#144

[dfed]

Great!! AVAudioPCMBuffer is easier for me to work with anyways 😄