Media: Eliminate NPE from race conditions

Race conditions may happen between
MediaSessionManager.SessionsChangedWrapper.release() and calling
onActiveSessionsChanged(), which might cause NPE. Copies member
variables as local variables to prevent that.

Test: cts-tradefed run cts -m MediaTest
Bug: 62841633
Change-Id: I69b6d155a1a5c475ab4bb317b60baa6f3a030e5a
1 file changed