Fix cursor not updated after clicking internal link

updateCursor() was called by wheelEvent(), which made sense,
because after the wheel event the page will have moved under the cursor.

With smooth scrolling, it makes less sense in wheelEvent(),
because at that point scrolling is still in the future.

scrollContentsBy() appears to be called on every scroll step.
(It is documented to be called at scrollbar value changes, so makes sense.)

This patch removes updateCursor() from wheelEvent(), but adds it to scrollContentsBy().

I did not check anything out with d->visibleItems, as was indicated it !176.

BUG: 421437