Fix 2532504 - fix NPE in AllApps3D.onKeyDown.

Change-Id: I8fba9b0b5217d630d84a6a260865d454db2bb046
diff --git a/src/com/android/launcher2/AllApps3D.java b/src/com/android/launcher2/AllApps3D.java
index 5b17b10..8467b39 100644
--- a/src/com/android/launcher2/AllApps3D.java
+++ b/src/com/android/launcher2/AllApps3D.java
@@ -809,8 +809,12 @@
         }
     }
 
+    /**
+     * If sRollo is null, then we're not visible.  This is also used to guard against
+     * sRollo being null.
+     */
     public boolean isVisible() {
-        return mZoom > 0.001f;
+        return sRollo != null && mZoom > 0.001f;
     }
 
     public boolean isOpaque() {