Problem: -1 used for invalid socket

Solution: use retired_fd instead

src/ipc_connecter.cpp

@@ -115,7 +115,7 @@ int zmq::ipc_connecter_t::open ()
 
     //  Create the socket.
     _s = open_socket (AF_UNIX, SOCK_STREAM, 0);
-    if (_s == -1)
+    if (_s == retired_fd)
         return -1;
 
     //  Set the non-blocking flag.

src/tipc_connecter.cpp

@@ -116,7 +116,7 @@ int zmq::tipc_connecter_t::open ()
     }
     //  Create the socket.
     _s = open_socket (AF_TIPC, SOCK_STREAM, 0);
-    if (_s == -1)
+    if (_s == retired_fd)
         return -1;
 
     //  Set the non-blocking flag.

src/tipc_listener.cpp

@@ -102,7 +102,7 @@ int zmq::tipc_listener_t::set_local_address (const char *addr_)
 
     //  Create a listening socket.
     _s = open_socket (AF_TIPC, SOCK_STREAM, 0);
-    if (_s == -1)
+    if (_s == retired_fd)
         return -1;
 
     // If random Port Identity, update address object to reflect the assigned address