fix #1928

LIST should not return ERR_NOSUCHCHANNEL for nonexistent channels

irc/handlers.go

 		for _, chname := range channels {
 			channel := server.channels.Get(chname)
 			if channel == nil || (!clientIsOp && channel.flags.HasMode(modes.Secret) && !channel.hasClient(client)) {
-				if len(chname) > 0 {
-					rb.Add(nil, server.name, ERR_NOSUCHCHANNEL, client.nick, utils.SafeErrorParam(chname), client.t("No such channel"))
-				}
 				continue
 			}
 			if matcher.Matches(channel) {