PaymentVariantsWindow: Disable calcualte button when save button is enabled

Elwig/Windows/PaymentVariantsWindow.xaml.cs

@@ -134,6 +134,7 @@ namespace Elwig.Windows {
                 (ConsiderPenaltiesInput.IsChecked != BillingData?.ConsiderContractPenalties) ||
                 (ConsiderPenaltyInput.IsChecked != BillingData?.ConsiderTotalPenalty) ||
                 (ConsiderAutoInput.IsChecked != BillingData?.ConsiderAutoBusinessShares));
+            CalculateButton.IsEnabled = !SaveButton.IsEnabled && PaymentVariantList.SelectedItem is PaymentVar { TestVariant: true };
         }
 
         private void UpdateSums() {