Fix update passing wrong Tree to content in pop widget

widget/src/pop.rs

@@ -127,7 +127,14 @@ where
         }
 
         self.content.as_widget_mut().update(
-            tree, event, layout, cursor, renderer, clipboard, shell, viewport,
+            &mut tree.children[0],
+            event,
+            layout,
+            cursor,
+            renderer,
+            clipboard,
+            shell,
+            viewport,
         );
     }