message: Fix segfault
  In async_connect callback, err was clear, but socket->set_option
  threw "Bad file descriptor". This caused a segfault.
  Side effect of this fix: sometimes a log entry like this shows up. This
  happens when it would have faulted.
  ```
  connection failed to localhost:9002: Undefined error: 0
  ```
diff: @@ -1943,7 +1943,7 @@ namespace eosio {
  c->socket->async_connect( current_endpoint, [weak_conn, endpoint_itr, this] ( const boost::system::error_code& err ) {
  auto c = weak_conn.lock();
  if (!c) return;
  - if( !err ) {
  + if( !err && c->socket->is_open() ) {
  start_session( c );
  c->send_handshake ();
  } else {
  