Fix synchronous connect failure for ipc://, tcp:// (LIBZMQ-294)

A synchronous connect() failure in ipc_connecter can result in Assertion
failed: s == retired_fd (ipc_connecter.cpp:174), as reported in LIBZMQ-294.

This patch fixes the bug, and also an identical problem in tcp_connecter
which has not hit people since TCP connect() usually completes via the
asynchronous code path (poll, out_event).
Signed-off-by: Martin Lucina <martin@lucina.net>

src/ipc_connecter.cpp

@@ -135,6 +135,7 @@ void zmq::ipc_connecter_t::start_connecting ()
     }
 
     //  Handle any other error condition by eventual reconnect.
+    close ();
     wait = true;
     add_reconnect_timer();
 }

src/tcp_connecter.cpp

@@ -146,6 +146,7 @@ void zmq::tcp_connecter_t::start_connecting ()
     }
 
     //  Handle any other error condition by eventual reconnect.
+    close ();
     wait = true;
     add_reconnect_timer();
 }