Volume dialog touch-tracking is disabled when in zenMute.

When simultaneously touch-sliding the volume dialog and using phone's
volume buttons, volume dialog could get into a weird state
where the volume dialog still thinks their is touch input after
entering/exiting zenMute.  This resulted in volume changes when using
the phone volume buttons but no change in the volume dialog UI. To
prevent this, the dialog will ensure there is no touch tracking
when it's in zenMute mode.

Bug: 30746594
Test: manual
Change-Id: I8f16d017d8e37ec7ff2f16df8f4997f64484412e