bugfix: fix the oldest message reference

src/plugins/sib-history-improved.js

@@ -71,7 +71,7 @@ converse.plugins.add('sib-history-improved', {
       log.debug(`Chatbox needs more messages, count: ${counter}`);
 
       const is_groupchat = data.chatbox.get('type') === converse.CHATROOMS_TYPE;
-      const oldest_message = messages.pop();
+      const oldest_message = messages[0] || null;
 
       if (oldest_message) {
         const by_jid = is_groupchat ? data.chatbox.get('jid') : _converse.bare_jid;