DeliveryAdminWindow: Use last scale error as default manual weighing reason

Elwig/Helpers/Utils.cs

@@ -219,8 +219,8 @@ namespace Elwig.Helpers {
                 .Sum();
         }
 
-        public static (int, string?)? ShowManualWeighingDialog() {
-            var d = new ManualWeighingDialog();
+        public static (int, string?)? ShowManualWeighingDialog(string? reason = null) {
+            var d = new ManualWeighingDialog(reason);
             return d.ShowDialog() == true ? (d.Weight, d.Reason) : null;
         }