Null out reference to RemoteAnimationTargets when animation finishes

Bug: 195430732
Test: Re-ran FallbackRecentsTest#testOverview, passes
Change-Id: If9be3429516caface998561fbcc8223e256d0fdf
diff --git a/quickstep/src/com/android/quickstep/views/RecentsView.java b/quickstep/src/com/android/quickstep/views/RecentsView.java
index ef52b41..853a3aa 100644
--- a/quickstep/src/com/android/quickstep/views/RecentsView.java
+++ b/quickstep/src/com/android/quickstep/views/RecentsView.java
@@ -4062,6 +4062,7 @@
         setCurrentTask(-1);
         mRecentsAnimationController = null;
         executeSideTaskLaunchCallback();
+        mRemoteTargetHandles = null;
     }
 
     public void setDisallowScrollToClearAll(boolean disallowScrollToClearAll) {