MailWindow: Return cleanly if WinziPrint fails 2

Elwig/Windows/MailWindow.xaml.cs

@@ -557,6 +557,8 @@ namespace Elwig.Windows {
                     PrintDocument = print;
                 } catch (Exception exc) {
                     MessageBox.Show(exc.Message, "Fehler", MessageBoxButton.OK, MessageBoxImage.Error);
+                    GenerateButton.IsEnabled = true;
+                    Mouse.OverrideCursor = null;
                     return;
                 }
             }