genlist: Remove weird behavior about item_show, bring_in

genlist: Remove weird behavior about item_show, bring_in

Summary:
When if item_show / bring_in is proceeded as 'deferred_show'
sequence, Scrollto_Type does not be checked perfectly.
As a result,
ELM_GENLIST_ITEM_SCROLLTO_NONE and any other integer values
are worked such as ELM_GENLIST_ITEM_SCROLLTO_BRING_IN.

As doxygen of Elm_Genlist_Item_Scrollto_Type,
ELM_GENLIST_ITEM_SCROLLTO_NONE and other incorrect number
should not work.

Fixes T4854

@fix

Reviewers: SanghyeonLee, woohyun, jpeg

Reviewed By: jpeg

Subscribers: id213sin, conr2d, cedric

Maniphest Tasks: T4854

Differential Revision: https://phab.enlightenment.org/D4684