Modify snippet in a WPF getting started (#1127)

dotnet-desktop-guide/net/wpf/get-started/snippets/create-app-visual-studio/csharp/Final.xaml.cs

@@ -28,7 +28,10 @@ namespace Names
         private void ButtonAddName_Click(object sender, RoutedEventArgs e)
         {
             if (!string.IsNullOrWhiteSpace(txtName.Text) && !lstNames.Items.Contains(txtName.Text))
+            {
                 lstNames.Items.Add(txtName.Text);
+                txtName.Clear();
+            }
         }
         //</FinalCode>
     }

dotnet-desktop-guide/net/wpf/get-started/snippets/create-app-visual-studio/vb/Final.xaml.vb

@@ -3,6 +3,7 @@
     Private Sub ButtonAddName_Click(sender As Object, e As RoutedEventArgs)
         If Not String.IsNullOrWhiteSpace(txtName.Text) And Not lstNames.Items.Contains(txtName.Text) Then
             lstNames.Items.Add(txtName.Text)
+            txtName.Clear()
         End If
     End Sub
     '</FinalCode>