Make MediaController#getSessionInfo() as @NonNull

Bug: 131069100
Test: atest CtsMediaTestCases:android.media.cts.MediaSessionTest;
      atest CtsMediaTestCases:android.media.cts.MediaControllerTest;
Change-Id: I5ecf04fd090dc684f5c7a84c1375de1639f7b4bd
2 files changed