Fix a bug in drop region.

isDescendantOf doesn't check equality, so add that

Bug: 154832406
Test: Put app in split-primary, open launcher search and drag
      app icon into top part of launcher
Change-Id: I737f4b2db88599e28ba8852341bbe37ae38c1239

services/core/java/com/android/server/wm/Task.java

@@ -2934,7 +2934,7 @@ class Task extends WindowContainer<WindowContainer> {
             final Task rootTask = getRootTask();
             final Task topNonOrgTask =
                     rootTask.mCreatedByOrganizer ? rootTask.getTopMostTask() : rootTask;
-            if (isDescendantOf(topNonOrgTask)) {
+            if (this == topNonOrgTask || isDescendantOf(topNonOrgTask)) {
                 return false;
             }
         }