Do not process presence updates as GC1.0 joins
I had an IRC channel MUC history duplication issue once again. Seems like yaxim sent a presence update in the morning, some time after the IRC server was restarted, and biboumi treated it as a join:
2019-11-12_07:05:57.95514 [DEBUG]: src/xmpp/xmpp_component.cpp:162: XMPP RECEIVING: <presence from="georg@domain/yaxim" id="F6PA5-62647" to="#firstname.lastname@example.org/nickname"> <status /> <priority>-10</priority> <c xmlns="http://jabber.org/protocol/caps" hash="sha-1" node="https://yaxim.org/" ver="PNyKvAFdHcM4HyMVijywvPee9+o="/> </presence>
Biboumi treated that as a join request and responded with a full MUC history. Due to #3392, it was not possible to deduplicate that, leading to doubled lines in the log.