elementary: gengrid - check the edge correctly

elementary: gengrid - check the edge correctly

Summary:
The routine of checking edge of left side, divide position by row.
Since the result of fisrt item of last line is 1, that item was not checked as edge.
This patch is for fixing it.

Test Plan:
elementary_test -to gengrid2
append items (about 6)
horizontal mode on and item loop enable
check item loop is working properly

Reviewers: cedric, jpeg, Hermet, SanghyeonLee

Subscribers: jehun.lim, SanghyeonLee, cedric, jpeg

Differential Revision: https://phab.enlightenment.org/D4358

Change-Id: I60331e6ad537a4114000bca0ca59e91aa3ac1c75
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>