[advancedsettings.xml] Report an error if invalid characters are found

[bugwelle]

If I have these lines in my advancedsettings.xml, then MediaElch will fail to use any genre after the first &:

	<genres>
		<map from="Aaa" to="Bbb" />
		<map from="Action & Adventure" to="Ação & Aventura" />
		<map from="Animation" to="Animação" />
	</genres>

Reason: & needs to be escaped as &. MediaElch silently ignores all tags after the first &. We don't do any error reporting...