mp3dec: handle EOS with first frame am: b37379401f am: 9a1b7cac37 am: f9cd369204 am: 8b5c703279

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/av/+/12104882

Change-Id: I431fde8c62b2914d88348d528e61068b53bf3706