MinGWでビルドが通らなくなっていたので修正

- error: passing argument 3 of 'SetWindowLongPtrW' makes integer
   from pointer without a cast [-Wint-conversion]
- error: incompatible pointer to integer conversion passing 'void *'
   to parameter of type 'LONG_PTR' (aka 'long long') [-Wint-conversion]
- 56367b9

ttssh2/ttxssh/ttxssh.c

@@ -1369,7 +1369,7 @@ static INT_PTR CALLBACK TTXHostDlg(HWND dlg, UINT msg, WPARAM wParam, LPARAM lPa
 	case WM_DESTROY:
 		ComPortInfoFree(dlg_data->ComPortInfoPtr, dlg_data->ComPortInfoCount);
 		free(dlg_data);
-		SetWindowLongPtrW(dlg, DWLP_USER, NULL);
+		SetWindowLongPtrW(dlg, DWLP_USER, 0);
 		break;
 	}
 	return FALSE;