fix QUIT: "channels" shouldn't contain all channels of the bot

[christianrank]

channels should only contain channels where the quitting user was joined, not all the channels the bot is connected to

[Zoddo]

Nobody to merge this PR?

[vBm]

@Zoddo Code doesn't match style for starters (brace is on it's own line while rest in the file it isn't, code should be consistent) would be my guess why it hasn't been merged yet.

ping @jirwin to shed some light on the topic :)

[jirwin]

Thanks for this. I merged #448 and I believe it covers the same issue.

[davericher]

+1