Bug 1504: Wrong message when setting TransferOptions.OverwriteMode property to an invalid value

https://winscp.net/tracker/1504

Source commit: ad16a25e175ce048a18cef82165cead9767e6e48

dotnet/TransferOptions.cs

@@ -103,7 +103,7 @@ namespace WinSCP
                     switches.Add(Session.FormatSwitch("append"));
                     break;
                 default:
-                    throw new ArgumentException(string.Format(CultureInfo.CurrentCulture, "{0} is not supported", TransferMode));
+                    throw new ArgumentException(string.Format(CultureInfo.CurrentCulture, "{0} is not supported", OverwriteMode));
             }
 
             return string.Join(" ", switches.ToArray());