message: Forgotten method's return
diff: @@ -84,6 +84,7 @@ AsyncOpenTask::register_download_progress_notifier(std::function<SyncSession::Pr
  if (auto session = m_session.load()) {
  auto token = session->register_progress_notifier(callback, SyncSession::ProgressDirection::download, false);
  m_registered_callbacks.emplace_back(token);
  + return token;
  }
  else {
  return 0;
  