Clear ref after animation if visual stashing not supported

Bug: 206814323
Test: Presubmit
Change-Id: Ia38bd2707edbddf1b1f2ad98b3cdac4c8c62a6d3
diff --git a/quickstep/src/com/android/launcher3/taskbar/TaskbarStashController.java b/quickstep/src/com/android/launcher3/taskbar/TaskbarStashController.java
index acb4aa8..60842c8 100644
--- a/quickstep/src/com/android/launcher3/taskbar/TaskbarStashController.java
+++ b/quickstep/src/com/android/launcher3/taskbar/TaskbarStashController.java
@@ -282,6 +282,12 @@
             // Just hide/show the icons instead of stashing into a handle.
             mAnimator.play(mIconAlphaForStash.animateToValue(isStashed ? 0 : 1)
                     .setDuration(duration));
+            mAnimator.addListener(new AnimatorListenerAdapter() {
+                @Override
+                public void onAnimationEnd(Animator animation) {
+                    mAnimator = null;
+                }
+            });
             return;
         }