don't show [+] on leaves

plugins/ui-designer/ui-designer-new/src/com/intellij/designer/componentTree/TreeContentProvider.java

@@ -82,6 +82,11 @@ public final class TreeContentProvider extends AbstractTreeStructure {
     return false;
   }
 
+  @Override
+  public boolean isAlwaysLeaf(Object element) {
+    return element instanceof RadComponent && ((RadComponent)element).getChildren().isEmpty();
+  }
+
   @Override
   public boolean hasSomethingToCommit() {
     return false;