Merge "MediaMuxer:Avoid hang during stop() on empty track" into rvc-qpr-dev am: e01df89d9e am: 55f730f7c1

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/av/+/12701960

Change-Id: Ic213b9768a193a35122d9ca2300469ff135b7ebd