Merge "Improve validation of channel indices in pcmDmx." into sc-dev am: 38afdcc7d0 am: 740116e266 am: a74df9ebb7

Original change: https://googleplex-android-review.googlesource.com/c/platform/external/aac/+/14373123

Change-Id: Ide9f04a86ffe263be10713cd77e2edb44b1b5b0e