Fix NPE

Bug: 6329157
Change-Id: Idd2db78890d196bcbfbe93640e07a96037638341
diff --git a/src/com/android/launcher2/AppsCustomizeTabHost.java b/src/com/android/launcher2/AppsCustomizeTabHost.java
index 0199d01..0c5bbeb 100644
--- a/src/com/android/launcher2/AppsCustomizeTabHost.java
+++ b/src/com/android/launcher2/AppsCustomizeTabHost.java
@@ -436,6 +436,8 @@
 
     private void setVisibilityOfSiblingsWithLowerZOrder(int visibility) {
         ViewGroup parent = (ViewGroup) getParent();
+        if (parent == null) return;
+
         final int count = parent.getChildCount();
         if (!isChildrenDrawingOrderEnabled()) {
             for (int i = 0; i < count; i++) {