Fix disco bounce crash
b/30413641

Change-Id: Icb2f3f11024daa78c3f59cab8c773091b9481feb
diff --git a/src/com/android/launcher3/allapps/AllAppsTransitionController.java b/src/com/android/launcher3/allapps/AllAppsTransitionController.java
index eb6c926..7eef2dd 100644
--- a/src/com/android/launcher3/allapps/AllAppsTransitionController.java
+++ b/src/com/android/launcher3/allapps/AllAppsTransitionController.java
@@ -432,6 +432,9 @@
         mAppsView.post(new Runnable() {
             @Override
             public void run() {
+                if (mDiscoBounceAnimation == null) {
+                    return;
+                }
                 mDiscoBounceAnimation.start();
             }
         });