Fix composer tag parsing in mp4 am: 943e41be15 am: 6baefed30d am: 3b22012e64 am: 20eb928ce8

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/av/+/12109660

Change-Id: I2c81e83639434ba591e0597c444f02f9fcd2b22c