Viewport should zoom out when screen magnification is disabled.

1. If screen magnification is disabled when the screen is in a
   magnified state we have to zoom out since otherwise the user
   is stuck in a magnified state without ability to pan/zoom/
   toggle magnification which renders the device useless.

bug:7131030

Change-Id: I8f3339f31310448ec8742f3101c1fdc61a6a5f83