Fix tbody row offset for HTMLTableElement.extract
Fix tbody row offset for HTMLTableElement.extract

Pushed 6a52096 a bit hastily: the tbody/header fallback didn't adjust
the beginning index of the first entry loop when collecting results,
meaning column headers were also being included in the results array.

Alhadis/Snippets,Alhadis/Snippets,Alhadis/Snippets,Alhadis/Snippets,Alhadis/Snippets