Remove dead links from the list of all links

Fix segfault that occurs when bip admin users use:
/BIP DEL_CONN <connection name>
/BIP ADD_CONN <connection name> <network>

Closes #325

src/irc.c

@@ -2625,6 +2625,8 @@ void link_kill(bip_t *bip, struct link *link)
 	while ((ci = list_remove_first(&link->chan_infos_order)))
 		free(ci);
 
+	list_remove(&bip->link_list, link);
+
 	MAYFREE(link->username);
 	MAYFREE(link->realname);
 	MAYFREE(link->s_password);