elm_genlist: fix highlighted items overlap with group item during scrolling and focus...

elm_genlist: fix highlighted items overlap with group item during scrolling and focus when intersect.

Summary: Highlighted genlist item overlap with group item during scrolling and focus when itersect.

Test Plan:
Run elementary_test.
	   open Genlist Group.
	   select one item and try to cross the group item via scrolling.
	   Highlighted item comes over group item.

Reviewers: Hermet, raster, cedric

Reviewed By: cedric

Subscribers: rajeshps, govi, poornima.srinivasan, shilpasingh

Differential Revision: https://phab.enlightenment.org/D2640

Signed-off-by: Cedric BAIL <cedric@osg.samsung.com>