[dvipdfmx] unknown options not reported when reading stdin

[Karl Berry]

Certainly agreed, cmdline settings should override what's in the file,
but it doesn't seem like that absolutely requires reading the file
before processing the cmdline. I can see how it would have been
convenient to implement it that way, but it's not like there's no other
way to do it. Anyway, not a big deal, just struck me as unusual. --best,karl.