List scrolling backwards with hasVariableItemDimensions causes item renderers to shift

[wman1980]

Hi,

there is a small issue with list component and hasVariableItemDimensions.

Starting point is a list and a simple item renderer and each of the item renderer has a different height. Scrolling down of list is fine, but scrolling up produces some visual issues.
It looks like the bounds of the list to add/remove item renderer are calculated wrong and the list starts jumping while scrolling.

Further details can be found here http://forum.starling-framework.org/topic/bug-with-feathers-list-and-hasvariableitemdimensions?replies=1#post-25765

Regards,
wman