Fixing another reference to Launcher activity after its destruction

Bug: 139137636
Change-Id: Id7a3a3d8c49d28dae964852661dfa330a8535375
diff --git a/quickstep/src/com/android/launcher3/LauncherAnimationRunner.java b/quickstep/src/com/android/launcher3/LauncherAnimationRunner.java
index 96ac489..31c1acf 100644
--- a/quickstep/src/com/android/launcher3/LauncherAnimationRunner.java
+++ b/quickstep/src/com/android/launcher3/LauncherAnimationRunner.java
@@ -55,7 +55,10 @@
             RemoteAnimationTargetCompat[] wallpaperTargets, Runnable runnable) {
         Runnable r = () -> {
             finishExistingAnimation();
-            mAnimationResult = new AnimationResult(runnable);
+            mAnimationResult = new AnimationResult(() -> {
+                runnable.run();
+                mAnimationResult = null;
+            });
             onCreateAnimation(appTargets, wallpaperTargets, mAnimationResult);
         };
         if (mStartAtFrontOfQueue) {