modes: Return right character on unknown mode char

irc/modes.go

 		if (op == Add) || (op == Remove) {
 			modeArg = modeArg[1:]
 		} else {
-			client.Send(nil, server.nameString, ERR_UNKNOWNMODE, client.nickString, string(modeArg[1]), "is an unknown mode character to me")
+			client.Send(nil, server.nameString, ERR_UNKNOWNMODE, client.nickString, string(modeArg[0]), "is an unknown mode character to me")
 			return false
 		}
 
 		if (op == Add) || (op == Remove) {
 			modeArg = modeArg[1:]
 		} else {
-			client.Send(nil, server.nameString, ERR_UNKNOWNMODE, client.nickString, string(modeArg[1]), "is an unknown mode character to me")
+			client.Send(nil, server.nameString, ERR_UNKNOWNMODE, client.nickString, string(modeArg[0]), "is an unknown mode character to me")
 			return false
 		}