Fixed a crash when opening the conflicts dialog (#8005)

Author: gave92

src/Files/Dialogs/FilesystemOperationDialog.xaml.cs

@@ -42,7 +42,10 @@ protected override void OnApplyTemplate()
         private void PrimaryButton_GotFocus(object sender, RoutedEventArgs e)
         {
             (sender as Button).GotFocus -= PrimaryButton_GotFocus;
-            chkPermanentlyDelete.IsEnabled = ViewModel.PermanentlyDeleteEnabled;
+            if (chkPermanentlyDelete != null)
+            {
+                chkPermanentlyDelete.IsEnabled = ViewModel.PermanentlyDeleteEnabled;
+            }
             DetailsGrid.IsEnabled = true;
         }