Fix progress of VolumePanel never refresh

On some occasions when disconnecting a headset it is possible for
the volume slider to enter a state where it is no longer updates.

The cause was that ProgressBar enters a state where a call to
doRefreshProgress no longer updates the progress.

The solution was to make sure mRefreshIsPosted is set to false
when mRefreshProgressRunnable is removed.

Change-Id: I1929e4916a582d09a7ec4911eb4f0052ad7a51ba