UpdateDialog: Fix cancellation and buttons

Elwig/Dialogs/UpdateDialog.xaml.cs

@@ -3,6 +3,7 @@ using System;
 using System.Diagnostics;
 using System.IO;
 using System.Net.Http;
+using System.Threading;
 using System.Threading.Tasks;
 using System.Windows;
 using System.Windows.Navigation;
@@ -13,36 +14,47 @@ namespace Elwig.Dialogs {
         public string Version { get; private set; }
         public string Url { get; private set; }
 
+        private readonly CancellationTokenSource Cancellation;
+
         public UpdateDialog(string version, string url, long size) {
             Version = version;
             Url = url;
+            Cancellation = new();
             InitializeComponent();
             VersionText.Text = version;
             SizeText.Text = $"{size / 1024 / 1024}";
         }
 
+        private void OnClosed(object sender, EventArgs evt) {
+            Cancellation.Cancel();
+        }
+
         private async void InstallButton_Click(object sender, RoutedEventArgs evt) {
             Description.Visibility = Visibility.Hidden;
             ProgressBar.Visibility = Visibility.Visible;
             InstallButton.IsEnabled = false;
             await Install();
-            DialogResult = true;
             Close();
         }
 
         public async Task Install() {
             var fileName = Path.Combine(App.TempPath, $"Elwig-{Version}.exe");
-            {
+            try {
                 using var stream = new FileStream(fileName, FileMode.Create);
                 using var client = new HttpClient() {
                     Timeout = TimeSpan.FromSeconds(5),
                 };
                 await client.DownloadAsync(Url, stream, new Progress<double>(p => {
                     ProgressBar.Value = p * 100.0;
-                }));
+                }), Cancellation.Token);
+            } catch (OperationCanceledException) {
+                File.Delete(fileName);
+                return;
+            } catch (Exception exc) {
+                MessageBox.Show(exc.Message, "Fehler", MessageBoxButton.OK, MessageBoxImage.Error);
             }
-
             Process.Start(fileName);
+            DialogResult = true;
         }
 
         private void Hyperlink_RequestNavigate(object sender, RequestNavigateEventArgs e) {