SystemUI: Fix potential NPE

Does already cause issues on some Halo ports to other ROMs.
Might not cause issues on PA (yet), but better safe than sorry.
Camera Tile : Close on flip/switch

Currently the camera tile only checks whether the
container panel is fully expanded. This doesnt take into account
when the user swipes to another panel via handle bar swipe, or by
pressing the switch button in the top right of the drawer.

Reproduction steps :
    Go to quick settings panel
    Enable camera tile
    Switch to notifications via swipe or switch button
    Camera preview stays persistent behind drawer

This patchset also makes the view hierarchy lookups one time, rather than
on each runnable run which is quite frequent (100ms).

Change-Id: Ic803744b63613d1e58b3efd4a92d052a16e5a2bd