UI: Don't show sub-item SpacingHelper on locked group

UI/window-basic-preview.cpp

@@ -2467,6 +2467,12 @@ void OBSBasicPreview::DrawSpacingHelpers()
 	if (itemSize.x == 0.0f || itemSize.y == 0.0f)
 		return;
 
+	obs_sceneitem_t *parentGroup =
+		obs_sceneitem_get_group(main->GetCurrentScene(), item);
+
+	if (parentGroup && obs_sceneitem_locked(parentGroup))
+		return;
+
 	matrix4 boxTransform;
 	obs_sceneitem_get_box_transform(item, &boxTransform);