Do not execute controller callbacks, if controller is null

Bug: 109812478
Change-Id: I55adc276fd894dd5f8913483984266327d7d482b

quickstep/src/com/android/quickstep/RecentsAnimationWrapper.java

@@ -49,6 +49,9 @@ public class RecentsAnimationWrapper {
         this.mController = controller;
         this.targetSet = targetSet;
 
+        if (controller == null) {
+            return;
+        }
         if (mInputConsumerEnabled) {
             enableInputConsumer();
         }