Bugfixes (hopefully :))

I had two bugs:
 - sometimes somehow rootScrollHeight and el.scrollHeight became 0, in which case the body was scrolled instead of the overflowing ancestor
 - the other bug involves the pending and queue mechanism: it only works if the scrolling elem stays the same. But that not always the case: for example the user scrolling an overflowing div then moves the cursor outside of the div and wants to scroll the body, but the div is scrolled (if it can, if it is already at the end then no scrolling happens)

I fixed them, hopefully :)