MusicFxHelper: avoid modify AudioSession list while iterating am: bf59e7edd4 am: c4c78b904f

Original change: https://android-review.googlesource.com/c/platform/frameworks/base/+/2869795

Change-Id: Ief4e1bf0985b091177a29f07f504b4301b0125ed
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>