add result->error_msg for new CONTROLLER_TIMED_OUT (#4341)

Signed-off-by: Mike Wake <[email protected]>

nav2_controller/src/controller_server.cpp

@@ -566,6 +566,7 @@ void ControllerServer::computeControl()
     onGoalExit();
     std::shared_ptr<Action::Result> result = std::make_shared<Action::Result>();
     result->error_code = Action::Result::CONTROLLER_TIMED_OUT;
+    result->error_msg = e.what();
     action_server_->terminate_current(result);
     return;
   } catch (nav2_core::ControllerException & e) {