a follow-up fix for the previous commit.

Author: agentzh

src/ngx_http_lua_socket_udp.c

@@ -1358,7 +1358,7 @@ ngx_http_lua_udp_connect(ngx_udp_connection_t *uc)
 
     ngx_log_debug1(NGX_LOG_DEBUG_EVENT, &uc->log, 0, "UDP socket %d", s);
 
-    if (s == -1) {
+    if (s == (ngx_socket_t) -1) {
         ngx_log_error(NGX_LOG_ALERT, &uc->log, ngx_socket_errno,
                       ngx_socket_n " failed");