Fix crash when handling recents animation canceled

- If Launcher finishes the animation, that also cleans up the screenshot
  on the server side, so we can skip calling it

Fixes: 192684578
Test: N/a, adding a null check
Change-Id: Ia6b99b4262e72f925e7d622ea8833d3c88252633
diff --git a/quickstep/src/com/android/quickstep/GestureState.java b/quickstep/src/com/android/quickstep/GestureState.java
index a302a07..385b3b4 100644
--- a/quickstep/src/com/android/quickstep/GestureState.java
+++ b/quickstep/src/com/android/quickstep/GestureState.java
@@ -364,7 +364,9 @@
         mStateCallback.setState(STATE_RECENTS_ANIMATION_ENDED);
         if (mRecentsAnimationCanceledSnapshot != null) {
             // Clean up the screenshot to finalize the recents animation cancel
-            mRecentsAnimationController.cleanupScreenshot();
+            if (mRecentsAnimationController != null) {
+                mRecentsAnimationController.cleanupScreenshot();
+            }
             mRecentsAnimationCanceledSnapshot = null;
         }
     }