message: Properly clean up state in MM actor, close
diff: @@ -71,6 +71,12 @@ middleman_actor_impl::middleman_actor_impl(actor_config& cfg,
  void middleman_actor_impl::on_exit() {
  CAF_LOG_TRACE("");
  broker_ = nullptr;
  + cached_tcp_.clear();
  + cached_udp_.clear();
  + for (auto& kvp : pending_)
  + for (auto& promise : kvp.second)
  + promise.deliver(make_error(sec::cannot_connect_to_node));
  + pending_.clear();
  }
  const char* middleman_actor_impl::name() const {
  