Fixes NPE in AbsSwipeUpHandler.

Fixes: 187243410
Test: Manual (not sure of exact repro steps, but I was hitting it
before installing - though reinstall itself may have fixed it).

Change-Id: I7510a675da9d2c1a484da8e00ca856f19445025c

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

@@ -1705,7 +1705,7 @@ public abstract class AbsSwipeUpHandler<T extends StatefulActivity<S>,
         // No need to apply any transform if there is ongoing swipe-pip-to-home animator since
         // that animator handles the leash solely.
         if (mRecentsAnimationTargets != null && !mIsSwipingPipToHome) {
-            if (mRecentsViewScrollLinked) {
+            if (mRecentsViewScrollLinked && mRecentsView != null) {
                 mTaskViewSimulator.setScroll(mRecentsView.getScrollOffset());
             }
             mTaskViewSimulator.apply(mTransformParams);