elm_gengrid: fix missing variable initialization.
elm_gengrid: fix missing variable initialization.

Summary:
- item's still_in variable is not initialized.

@fix

Reviewers: seoz, singh.amitesh, raster, SanghyeonLee

Reviewed By: SanghyeonLee

Differential Revision: https://phab.enlightenment.org/D2871

tasn/elementary,FlorentRevest/Elementary,rvandegrift/elementary,FlorentRevest/Elementary,rvandegrift/elementary,FlorentRevest/Elementary,tasn/elementary,rvandegrift/elementary,FlorentRevest/Elementary,tasn/elementary,rvandegrift/elementary,tasn/elementary,tasn/elementary