Reset alpha of media when not fading

Since the QSAnimator can run even when QS is not visible, the media host
could be set to alpha 0 when rotated to landscape, and never reset to 1
once rotated back to portrait. So, this explicitly resets the alpha if the
animation builder is being set up in portrait mode.

Fixes: 192939241
Test: follow repro steps in bug, observe media visible
Change-Id: Ice6087b0d2dee0a575003bb888c93ea91cee931a