Fix launcher crash by set divider hidden

We will hide divider when isLikelyToStartNewTask become true, but
this call sometime earlier than onRecentsAnimationStart then cause
crash because mRecentsAnimationTargets is still null.

Fix this by checking mRecentsAnimationTargets before set divider
visibility. And also add new condition to hide divider to ensure
it hidden if such case happened.

Fix: 265238266
Test: manaul
Test: pass existing tests
Change-Id: I80b1294e69a52e7ac5255cd8e55e7c5e6a3dcbcb

quickstep/src/com/android/quickstep/AbsSwipeUpHandler.java

@@ -324,6 +324,7 @@ public abstract class AbsSwipeUpHandler<T extends StatefulActivity<S>,
     // May be set to false when mIsTransientTaskbar is true.
     private boolean mCanSlowSwipeGoHome = true;
     private boolean mHasReachedOverviewThreshold = false;
+    private boolean mDividerHiddenBeforeAnimation = false;
 
     @Nullable
     private RemoteAnimationTargets.ReleaseCheck mSwipePipToHomeReleaseCheck = null;
@@ -1677,7 +1678,8 @@ public abstract class AbsSwipeUpHandler<T extends StatefulActivity<S>,
         mRecentsAnimationController.enableInputConsumer();
 
         // Start hiding the divider
-        if (!mIsTransientTaskbar || mTaskbarAlreadyOpen || mIsTaskbarAllAppsOpen) {
+        if (!mIsTransientTaskbar || mTaskbarAlreadyOpen || mIsTaskbarAllAppsOpen
+                || mDividerHiddenBeforeAnimation) {
             setDividerShown(false /* shown */, true /* immediate */);
         }
     }
@@ -2327,6 +2329,12 @@ public abstract class AbsSwipeUpHandler<T extends StatefulActivity<S>,
     }
 
     private void setDividerShown(boolean shown, boolean immediate) {
+        if (mRecentsAnimationTargets == null) {
+            if (!shown) {
+                mDividerHiddenBeforeAnimation = true;
+            }
+            return;
+        }
         if (mDividerAnimator != null) {
             mDividerAnimator.cancel();
         }