Fix occasional failure to disable navbar

If the observer in PSB fires before that in WM, then WM.hasNavigationBar() would still be true. When ored with the System.Setting, which should be false at that time, would not remove the navbarview.

TODO: handle navbar state outside of WM with a broadcast from WM, rather than letting other things use the system setting directly

Change-Id: Ie65f81bc6db4a1cac831755b0b8c39db386d95dd