Fix placeholder not shown after launch again

This issue is regressed by [1].
When we verify if the container is top active container,
we should filter out the case that the Activity is not in
TaskFragmentContainer.

fixes: 224431790
Test: manual - test steps mentioned in bug

[1]: 3d419be76f

Change-Id: Iae3b2b903bf15448d429b8edd25ceeef97e74738

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

@@ -501,7 +501,7 @@ public class SplitController implements JetpackTaskFragmentOrganizer.TaskFragmen
         final  TaskFragmentContainer container = getContainerWithActivity(
                 activity.getActivityToken());
         // Don't launch placeholder if the container is occluded.
-        if (container != getTopActiveContainer()) {
+        if (container != null && container != getTopActiveContainer()) {
             return false;
         }