Hide IME adjust dims when divider is hidden

When locking the screen, the divider is hidden, but the ime
dims aren't if the ime doesn't go away. This makes sure that
the ime adjust-dims are hidden whenever the divider is.

Bug: 156775140
Test: Open ime for top-split, lock, then turn-on screen. Observe
      no dims on half the screen.
Change-Id: I0851edd0071649ed0fbf12c8cd4fa3055383d864