fixed bug with dimple height being incorrect

[MaikoHermans]

when the interItemSpacingY is set to 0 the dimple was being drawn to high because of the following line viewRect.origin.y -= additionalHeight * 2; by checking if the height is smaller or equal to 10 the accurate height can be given to the dimple.

also when the interItemSpacingY was set to a - value the dimple wouldn't draw like supposed to. this is also fixed with the added code