message: Catch exception by const reference
  Summary:
  As title.
  Pull Request resolved:
diff: @@ -39,7 +39,7 @@ void FileQLogger::setupStream() {
  folly::to<std::string>(path_, "/", (dcid.value()).hex(), extension);
  try {
  writer_ = std::make_unique<folly::AsyncFileWriter>(outputPath);
  - } catch (std::system_error err) {
  + } catch (const std::system_error& err) {
  LOG(ERROR) << "Error creating qlog file. " << err.what();
  return;
  }
  