Sanity check while updating volume in MediaRouteChooserDialog

Bug 6720224

When a window dies it's possible to receive a lingering ACTION_CANCEL
event to the SeekBar for volume. Be sure that we don't try to mess
with something that's already gone by that point.

Change-Id: I4f6119718fc21204d9013d591bc984b785b698b4
1 file changed