ConcurrentModificationException of RemoteVideoTrack.

[jinnyuri]

Describe the bug Sometime ConcurrentModificationException occurs, if multiple people exit a group call at the same time. I apologize for the lack of detailed logs, but describe solution below.

To Reproduce Steps to reproduce the behavior:

1. Make a group call.
2. Exit at same time.

Expected behavior Exception not occurs.

Screenshots If applicable, add screenshots to help explain your problem.

Device Info:

• Device: [e.g. Google Pixel 4] Galaxy S22, S23, etc.
• OS: [e.g. Android 12] All versions
• LiveKit SDK version: [e.g. 1.0.0] 2.1.1

Additional context Same as VideoTrack, if we apply lock for sinkVisibilityMap of RemoteVideoTrack, we can avoid the exception.

[davidliu]

Whoops, forgot to lock this down when I did the video track changes. Thanks for filing the issue.