bugfix: sslhandshake lost verify error when handshake completed immediately (#2506)

After ngx_ssl_handshake(c) returns NGX_OK, the handshake handler may
still record a verify error in u->error_ret via SSL_get_verify_result().
The old code only checked rc == NGX_ERROR and missed u->error_ret,
returning FFI_OK with an unread error.  Added u->error_ret != NULL check
so the Lua caller receives the SSL error instead of a misleading "closed"
on the next socket operation.

Author: tzssangglass

src/ngx_http_lua_socket_tcp.c

@@ -2035,7 +2035,7 @@ ngx_http_lua_ffi_socket_tcp_sslhandshake(ngx_http_request_t *r,
 
     ngx_http_lua_ssl_handshake_handler(c);
 
-    if (rc == NGX_ERROR) {
+    if (rc == NGX_ERROR || u->error_ret != NULL) {
         *errmsg = u->error_ret;
         return NGX_ERROR;
     }