message: Print warning to stderr when config file couldn't be opened.
diff: @@ -402,7 +402,8 @@ void Contour::executeAction(Action const& _action)
  [this](actions::OpenConfiguration) {
  auto const fileName = FileSystem::absolute(config_.backingFilePath);
  auto const cmd = fmt::format("{} \"{}\"", launcher(), fileName.string());
  - system(cmd.c_str());
  + if (system(cmd.c_str()) != EXIT_SUCCESS)
  + cerr << "Couldn't open configuration.\n";
  }
  }, _action);
  }
  