Fix UBSAN warning about applying zero offset to null pointer (#10700)

vpath may be NULL here so check for it before trying to add 0 (the length of the vpath) to it.

Author: Girgias

sapi/cli/php_cli_server.c

@@ -1785,8 +1785,10 @@ static int php_cli_server_client_read_request_on_message_complete(php_http_parse
 	php_cli_server_client *client = parser->data;
 	client->request.protocol_version = parser->http_major * 100 + parser->http_minor;
 	php_cli_server_request_translate_vpath(&client->request, client->server->document_root, client->server->document_root_len);
-	{
-		const char *vpath = client->request.vpath, *end = vpath + client->request.vpath_len, *p = end;
+	if (client->request.vpath) {
+		const char *vpath = client->request.vpath;
+		const char *end = vpath + client->request.vpath_len;
+		const char *p = end;
 		client->request.ext = end;
 		client->request.ext_len = 0;
 		while (p > vpath) {