Only set the id attribute if the controller was found

Co-authored-by: Hyunjin Song <tteu.ingog@gmail.com>

src/core/ControllerConnection.cpp

@@ -191,8 +191,11 @@ void ControllerConnection::saveSettings( QDomDocument & _doc, QDomElement & _thi
 		{
 			const auto& controllers = Engine::getSong()->controllers();
 			const auto it = std::find(controllers.begin(), controllers.end(), m_controller);
-			const int id = it != controllers.end() ? std::distance(controllers.begin(), it) : -1;
-			_this.setAttribute("id", id);
+			if (it != controllers.end())
+			{
+						const int id = std::distance(controllers.begin(), it);
+						_this.setAttribute("id", id);
+			}
 		}
 	}
 }