Base split action on focusedTaskView instead of runningTaskView

* getRunningTaskView() is null when rotating device,
only valid when swiping up to overview
* focusedTaskView() correctly set in both cases

Fixes: 199461147
Test: Bug doesn't repro
Change-Id: Ib39c1f6f05b3cd5f72c13facc6b8000346896476
diff --git a/quickstep/src/com/android/quickstep/views/RecentsView.java b/quickstep/src/com/android/quickstep/views/RecentsView.java
index dd470e8..3ed7b06 100644
--- a/quickstep/src/com/android/quickstep/views/RecentsView.java
+++ b/quickstep/src/com/android/quickstep/views/RecentsView.java
@@ -3150,7 +3150,7 @@
      */
     private void updateFocusedSplitButtonVisibility() {
         mActionsView.setSplitButtonVisible(mActivity.getDeviceProfile().isTablet &&
-                !(getRunningTaskView() instanceof GroupedTaskView) &&
+                !(getFocusedTaskView() instanceof GroupedTaskView) &&
                 getTaskViewCount() > 1
         );
     }