list: fix crash while setting nearest item in viewport
list: fix crash while setting nearest item in viewport

This is an example of classic code copy and paste mistake.
Probably inspired from similar code in genlist/gengrid.
We were actually deleting the other items (except selected one) in
viewport in _elm_list_nearest_visible_item_get() which results into crash
while deleting the list object.

@fix

Resolves: T2662

rvandegrift/elementary,rvandegrift/elementary,rvandegrift/elementary,rvandegrift/elementary