Fix NPE when calling updateStateLw

In multi-display environment, the existance of status bar and navigation
bar may differ per disply. In other words, we may not have status bar or
navigation bar on a external displays. Add null check to prevent this
NPE happens.

Test: WmTests
Fixes: 120779126

Change-Id: I805a061733cdbe09c5c1941a0f44e2e49964671a