irc client example doesn't handle JOIN responses from libera.chat

[ZXGuesser]

As reported here: https://spectrumcomputing.co.uk/forums/viewtopic.php?p=98334

libera.chat doesn't include a colon in the JOIN response (optional in the spec?) which makes the client drop the first character off the channel name it stores in memory.

The following ugly hack in ircsvrmsg.c cures it

	if(!strcmp(im->command, "JOIN"))
	{
		if (im->param[0] == ':') /* this is a horrible hack, de we need to check for optional : everywhere? */
			strlcpy(chan, (im->param)+1, CHANSZ);
		else
			strlcpy(chan, im->param, CHANSZ);
		setStatusLine(nick, chan);
		return;
	}