Prevent NPE when resetting divider bar visibility

Fix: 195325902
Test: atest
com.android.launcher3.memory.MemoryTests#testActivityRecreation
--rerun-until-failure

Change-Id: I12c48fe2834a225c5f7d042be632ddd29135b7c5
diff --git a/quickstep/src/com/android/quickstep/AbsSwipeUpHandler.java b/quickstep/src/com/android/quickstep/AbsSwipeUpHandler.java
index 6249e6a..42c89fd 100644
--- a/quickstep/src/com/android/quickstep/AbsSwipeUpHandler.java
+++ b/quickstep/src/com/android/quickstep/AbsSwipeUpHandler.java
@@ -1534,7 +1534,9 @@
         boolean wasVisible = mWasLauncherAlreadyVisible || mGestureStarted;
         mActivityInterface.onTransitionCancelled(wasVisible, mGestureState.getEndTarget());
 
-        TaskViewUtils.setDividerBarShown(mRecentsAnimationTargets.nonApps, true);
+        if (mRecentsAnimationTargets != null) {
+            TaskViewUtils.setDividerBarShown(mRecentsAnimationTargets.nonApps, true);
+        }
 
         // Leave the pending invisible flag, as it may be used by wallpaper open animation.
         if (mActivity != null) {