Fix music widget of LockScreen when Play Music has a error

When Play Music has a error and music stop playback,
LockScreen will try to register and unregister IRemoteControlDisplayWeak.
And, it cause music widget of LockScreen will flicker.

We try to check muisc is working by AudioManager to fix this issue.

Change-Id: If0df0042b03ccab6cec5fa6251a3d6c8601c2db7