Fix paging bug where if you go to a page and scroll down further than a previous (shorter) page can get to, the document is scrolled to bottom and looks empty.
#6
Used AI to figure this out after some back and forth, the 'ypos' function was not obvious.
Ideally I would add a feature that actually tracks the scroll position with the history, so you would go back to the line/page where you came from, preserving previous scrolling. The load (page,1) code in here doesn't reall do that as intended in light of the bugfix discovery.
Also improved the goto_link and goto_page dialog/feature so they handle bogus links and bogus URLs better.
