listview: Avoid a critical when reordering

When sorting a cell into the place its already at,
we were triggering criticals. Avoid that.

Fixes: #3180

gtk/gtklistitemwidget.c

@@ -629,10 +629,13 @@ gtk_list_item_widget_reorder_child (GtkListItemWidget *self,
         }
     }
 
+  if (child != sibling)
+    {
       gtk_widget_insert_after (child, widget, sibling);
       gtk_css_node_insert_after (gtk_widget_get_css_node (widget),
                                  gtk_widget_get_css_node (child),
                                  sibling ? gtk_widget_get_css_node (sibling) : NULL);
+    }
 }
 
 void