Fix disco bounce crash

b/30413641

Change-Id: Icb2f3f11024daa78c3f59cab8c773091b9481feb

src/com/android/launcher3/allapps/AllAppsTransitionController.java

@@ -432,6 +432,9 @@ public class AllAppsTransitionController implements TouchController, VerticalPul
         mAppsView.post(new Runnable() {
             @Override
             public void run() {
+                if (mDiscoBounceAnimation == null) {
+                    return;
+                }
                 mDiscoBounceAnimation.start();
             }
         });