Fix potential decrypt src pointer overflow. am: 9bae1251cf am: c732dd9227 am: 9078b155b9

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/av/+/13420866

MUST ONLY BE SUBMITTED BY AUTOMERGER

Change-Id: I54f1f0aa4deeb812afe926a0205dd3e9c856e0b1