SEO checklist output is not valid.

Hi,

SEO checklist output is not valid.

The variable $checked is setup wrongly with regard to its later use.
The resulting output is not valid.

Well, actually it is not even well-formed! :)

I spotted the problem serving my pages as XML, see #475242: Support Content-Type different from text/html
The attached patch fixes the defect.

Regards,
Antonio