Summary:
If user added item with item_insert_before and item_insert_after, item was not displayed.
For this reason, fixed box indicated item correctly from reference->button to VIEW(reference).
Additionally, remove the unused variable button in _Multibuttonentry_Item struct.
Reviewers: woohyun, CHAN, cedric, jpeg
Reviewed By: CHAN
Subscribers: cedric, jpeg
Differential Revision: https://phab.enlightenment.org/D4708