Fixed ZAP authentication

- if ZAP server returns anything except 200, connection is closed
- all security tests now pass correctly
- test_security_curve now does proper client key authentication using test key
- test_security_plain now does proper password authentication

src/curve_server.cpp

@@ -588,24 +588,28 @@ int zmq::curve_server_t::receive_and_process_zap_reply ()
 
     //  Address delimiter frame
     if (msg [0].size () > 0) {
+        rc = -1;
         errno = EPROTO;
         goto error;
     }
 
     //  Version frame
     if (msg [1].size () != 3 || memcmp (msg [1].data (), "1.0", 3)) {
+        rc = -1;
         errno = EPROTO;
         goto error;
     }
 
     //  Request id frame
     if (msg [2].size () != 1 || memcmp (msg [2].data (), "1", 1)) {
+        rc = -1;
         errno = EPROTO;
         goto error;
     }
 
     //  Status code frame
     if (msg [3].size () != 3 || memcmp (msg [3].data (), "200", 3)) {
+        rc = -1;
         errno = EACCES;
         goto error;
     }