portable service: fix clean shared memory, at_exit not called at flutter

Signed-off-by: 21pages <pages21@163.com>

flutter/lib/desktop/pages/connection_page.dart

@@ -90,6 +90,9 @@ class _ConnectionPageState extends State<ConnectionPage>
         Get.forceAppUpdate();
       }
       isWindowMinisized = false;
+    } else if (eventName == 'close') {
+      // called more then one time
+      bind.mainOnMainWindowClose();
     }
   }