Fix issue #6268190

Change-Id: Ib269fe34c4d3e704f4080076e173241c0761040c

Author: Dianne Hackborn

core/java/com/android/internal/widget/ActionBarOverlayLayout.java

@@ -137,7 +137,9 @@ protected boolean fitSystemWindows(Rect insets) {
 
         // The top and bottom action bars are always within the content area.
         boolean changed = applyInsets(mActionBarTop, insets, true, true, false, true);
-        changed |= applyInsets(mActionBarBottom, insets, true, false, true, true);
+        if (mActionBarBottom != null) {
+            changed |= applyInsets(mActionBarBottom, insets, true, false, true, true);
+        }
 
         // If the window has not requested system UI layout flags, we need to
         // make sure its content is not being covered by system UI...  though it