Fix event handlers in ControlUtils when new item is null

Elwig/Windows/MemberAdminWindow.xaml.cs

@@ -107,6 +107,7 @@ namespace Elwig.Windows {
                 DeliveryButton.IsEnabled = false;
                 ClearOriginalValues();
                 ClearInputs(validate);
+                ClearInputStates();
             }
             GC.Collect();
         }