pidgin/ljfisher-ssl-client-auth

Suppress error spews when we've left an IRC channel but the window is open.

My take on a patch from Florian Quèze to fix yet another IRC WHO problem.
#include "conversation.h"
PurpleAccount *purple_accounts_find_ext(const char *name, const char *protocol_id,
gboolean (*account_test)(const PurpleAccount *account));
PurpleAccount *purple_accounts_find_any(const char *name, const char *protocol);
PurpleAccount *purple_accounts_find_connected(const char *name, const char *protocol);