BOTS-29 : Fix Matrix-sent messages being echoed after netsplits.
BOTS-29 : Fix Matrix-sent messages being echoed after netsplits.

This was caused by not updating the nick correctly after *connecting*
to the IRC server (we already did on NICK messages).

matrix-org/matrix-appservice-irc,martindale/matrix-appservice-irc,matrix-org/matrix-appservice-irc,matrix-org/matrix-appservice-irc