Consider that the connect() succeded if errno EISCONN

Apparently on some systems, subsquent connect() calls may fail with EISCONN
error, to indicate that the connection succeded in the background, instead
of returning 0.

src/network/socket_handler.cpp

@@ -97,7 +97,8 @@ void SocketHandler::connect(const std::string& address, const std::string& port)
 
   for (struct addrinfo* rp = addr_res; rp; rp = rp->ai_next)
     {
-      if (::connect(this->socket, rp->ai_addr, rp->ai_addrlen) == 0)
+      if (::connect(this->socket, rp->ai_addr, rp->ai_addrlen) == 0
+          || errno == EISCONN)
         {
           log_info("Connection success.");
           this->connected = true;