Fix composer tag parsing in mp4 am: 943e41be15 am: 6baefed30d am: 51e1fa5916

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

Change-Id: I1d9adf3427c17aba1ee0527d3e5f17d9de7f171a