ListView can freeze if flicked beyond its bounds.

ListView can freeze if flicked beyond its bounds.

If the delegate's size changes in componentComplete and all
items are flicked out of view, an incorrect jump calculation
in addVisibleItems() resulted in a new delegate being created
in the wrong position, and retriggering the jump calculation,
which resulted in a new delegate being created in the wrong
position, and retriggering the jump...

Also fixed currentItem visibility.

Change-Id: Iad5f211c4fc5eed9c009d51a0ce3b58181a7b36e
Reviewed-by: Bea Lam <bea.lam@nokia.com>