Active container should contain non-finishing activity

Without this cl, the app will crash if a TaskFragment is closing when
the new top TaskFragment doesn't contain any non-finishing activity
(which should be closed later as well).

Before, when #cleanupContainer(), we will also update the new top active
container, but we didn't check if it contain any non finishing activity.

Fix: 212355346
Test: test with Settings with three finger click
Change-Id: I26538b85f1cf8e618a3f1ee6abada5a9f77f2b16

libs/WindowManager/Jetpack/src/androidx/window/extensions/embedding/SplitController.java

@@ -346,7 +346,7 @@ public class SplitController implements JetpackTaskFragmentOrganizer.TaskFragmen
     TaskFragmentContainer getTopActiveContainer() {
         for (int i = mContainers.size() - 1; i >= 0; i--) {
             TaskFragmentContainer container = mContainers.get(i);
-            if (!container.isFinished()) {
+            if (!container.isFinished() && container.getTopNonFinishingActivity() != null) {
                 return container;
             }
         }