Fix HTTPD protocol authentication

The HTTPD protocol mistakenly assumed that the `authenticator` parameter
of a listener would be NULL if the default authenticator is used.

Recent changes modified it so that the value is never NULL and
`NullAuthDeny` would be used for protocols which did not implement the
auth_default entry point.

server/core/service.c

@@ -272,7 +272,7 @@ serviceStartPort(SERVICE *service, SERV_LISTENER *port)
 
     memcpy(&(port->listener->func), funcs, sizeof(GWPROTOCOL));
 
-    const char *authenticator_name = "NullAuth";
+    const char *authenticator_name = "NullAuthDeny";
 
     if (port->authenticator)
     {