fix: error when menu key dynamic, close #6057

Author: tangjinzhou

components/menu/src/Menu.tsx

@@ -339,7 +339,7 @@ export default defineComponent({
     };
 
     const onInternalOpenChange = (key: Key, open: boolean) => {
-      const childrenEventKeys = keyMapStore.value[key].childrenEventKeys;
+      const childrenEventKeys = keyMapStore.value[key]?.childrenEventKeys || [];
       let newOpenKeys = mergedOpenKeys.value.filter(k => k !== key);
 
       if (open) {