Now:
{
	if(PQclientEncoding(conn) >= 0)
		/* Client is connected, you should use FromCharset here */
		return PQerrorMessage(conn);
	/* Client is disconnected, use system code page */
	return FromCharset(PQerrorMessage(conn));
}

Proposition:
{
	if(PQclientEncoding(conn) >= 0)
		return FromCharset(PQerrorMessage(conn))
	return FromSystemCharset(PQerrorMessage(conn));
}