VolumeDialogImpl: Respect multiple visible rows in landscape

If the user is in a call we are showing two volume rows, the default
(music) stream and the active stream, in this case the voice call.
Currently the second row is not touchable in landscape mode because
the calculation of the touchable region does not handle the case of
multiple visible rows.

This patchset adds a check wether the ringer drawer extra size is bigger
than the additionally visible rows and then substracts the size of the
visible rows so that they stay touchable.

Test: While receiving a call in landscape both, the music row and the
      ring row, are touchable. Touches at the left of the volume panel
      are still going through the app behind the volume panel.
Change-Id: Icda80b7a98d5510747bc92ef12a3c7647131b18d