Prevent infinite layout while hiding nav bar on keyguard

By the original logic, if there is a focused window which hides
navigation bar while keyguard is showing, PhoneWindowManager would
hide/show navigation bar frequently, which caused infinite layout.

Bug: 78681867
Test: 1. Open a photo in fullscreen mode (hiding navigation bar)
      2. Press power key to bring up keyguard
      3. See if there is "Performed 6 layouts in a row. Skipping" log

Change-Id: Id8c49ac8fc45b98294e48017308dce3117ed1cf8