tcp_connector fails to set the socket FD

The tcp_listener sets the socket FD when it accepts a connection. The tcp_connector on the other hand does not, leaving the FD to be -1.

diff --git a/src/tcp_connecter.cpp b/src/tcp_connecter.cpp
index 7d36d01..82110fc 100644
— a/src/tcp_connecter.cpp
+++ b/src/tcp_connecter.cpp
@@ -124,6 +125,9 @@ void zmq::tcp_connecter_t::out_event ()
tune_tcp_socket (fd);
tune_tcp_keepalives (fd, options.tcp_keepalive, options.tcp_keepalive_cnt, options.tcp_keepalive_idle, options.tcp_keepalive_intvl);

+ // remember our fd for ZMQ_SRCFD in messages
+ socket->set_fd(fd);
+
// Create the engine object for this connection.
stream_engine_t *engine = new (std::nothrow)
stream_engine_t (fd, options, endpoint);