Describe the bug

I recently noticed a gap in the history that AFAIK (but difficult to be sure) was caused by a new message being received before a MAM query was made. By the time the MAM query is made, it asks for messages newer than the last, and not for the messages before the last and after the previous message.

To Reproduce

Should be reproducible via a test.

Expected behavior

One possible solution is to add a filler for the gap, which can be clicked to fetch the missing messages. An alternative solution would be to make sure that MAM queries for the gap, and not newest messages.