MusicFxHelper: avoid modify AudioSession list while iterating am: bf59e7edd4

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

Change-Id: Ia52f5cfd1542a3c2fe493f81152e65dde8fe66ce
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>