Fix pop may call multiple times

lib/dialog/new_download_task_page.dart

@@ -115,6 +115,7 @@ class _NewDownloadTaskPage extends State<NewDownloadTaskPage> {
       WidgetsBinding.instance!.addPostFrameCallback((_) {
         context.canPop() ? context.pop() : context.go("/task_manager");
       });
+      _ok = false;
     }
     if (!_fetched) fetchDefaultCfg();
     final i18n = AppLocalizations.of(context)!;

lib/dialog/new_export_zip_task_page.dart

@@ -99,6 +99,7 @@ class _NewExportZipTaskPage extends State<NewExportZipTaskPage> {
       WidgetsBinding.instance!.addPostFrameCallback((_) {
         context.canPop() ? context.pop() : context.go("/task_manager");
       });
+      _ok = false;
     }
     if (!_fetched) fetchDefaultCfg();
     final i18n = AppLocalizations.of(context)!;

lib/dialog/new_user_page.dart

@@ -87,6 +87,7 @@ class _NewUserPage extends State<NewUserPage> {
       SchedulerBinding.instance.addPostFrameCallback((_) {
         context.canPop() ? context.pop() : context.go("/users");
       });
+      _newUserId = null;
       return Container();
     }
     final i18n = AppLocalizations.of(context)!;

lib/pages/login.dart

@@ -45,6 +45,7 @@ class _LoginPageState extends State<LoginPage>
   bool _isValid = false;
   bool _isLogin = false;
   bool _checkAuth = false;
+  bool _tryPoped = false;
 
   void _onStateChanged(dynamic _) {
     setState(() {});
@@ -120,10 +121,12 @@ class _LoginPageState extends State<LoginPage>
   Widget build(BuildContext context) {
     tryInitApi(context);
     _checkStatus(context);
-    if (isTop(context) && auth.user != null) {
+    if (isTop(context) && auth.user != null && !_tryPoped) {
       SchedulerBinding.instance.addPostFrameCallback((_) {
         context.canPop() ? context.pop() : context.go("/");
       });
+      _tryPoped = true;
+      return Container();
     }
     return Scaffold(
       appBar: AppBar(