[Om] tiny patch to CD XSLT code

[Dima]

Hi.

> Seems a sensible change (without knowing the background). I assume you
> are aware that unparsed-text-available() can return false for reasons
> other than non-existence of the file, for example if it contains
> characters not available in XML, or if it cannot be decoded as UTF-8.

  Thank you for answer. I have reviewed the semantics of unparsed-text-available()
at http://www.w3.org/TR/xslt20/ : it will return false if unparsed-text() would have failed
on the same file name argument. Which, after reviewing the use cases of the function
I've changed in OpenMath, seems fine to me ... But let the authors decide :)

Thanks, regards,
  Dima.

> Michael Kay
> Saxonica