NavigationBar: Fix NPE in NavigationBar

Change-Id: I4c1845775ca5ed39e53eaabb10ac13126628dc68
Signed-off-by: Mohammad Hasan Keramat J <ikeramat@protonmail.com>

packages/SystemUI/src/com/android/systemui/navigationbar/NavigationBar.java

@@ -1968,6 +1968,7 @@ public class NavigationBar extends ViewController<NavigationBarView> implements
     private void onBoundsChange() {
         // give wm some time to change fg app
         mHandler.postDelayed(() -> {
+            if (mView == null || !mView.isAttachedToWindow()) return;
             mWindowManager.updateViewLayout(mFrame, getBarLayoutParams(mContext.getResources()
                     .getConfiguration().windowConfiguration.getRotation()));
             mRegionSamplingHelper.updateSamplingRect();