len should be signed

src/conn.c

@@ -681,7 +681,8 @@ void xmpp_conn_disable_tls(xmpp_conn_t * const conn)
 static void _log_open_tag(xmpp_conn_t *conn, char **attrs)
 {
     char buf[4096];
-    size_t len, pos;
+    size_t pos;
+    int len;
     int i;
     
     if (!attrs) return;