Closes LIBZMQ-504.

This time correct backport from 3.x branch.

It was my mistake, sorry. Source in 3.x for reference:
tcp_connecter.cpp:172
https://github.com/zeromq/zeromq3-x/blob/master/src/tcp_connecter.cpp#L172

In 3.x zmq_connecter and tcp_connecter are merged, but code in almost the same.