elm_image: fix elm_image_memfile_set API fail when elm_image widget is not visible.
elm_image: fix elm_image_memfile_set API fail when elm_image widget is not visible.

Summary:
It could success only when the widget was visible.
The API must return EINA_TRUE if buffer and size has no problem, not visiblity of widget.
@fix

Reviewers: Hermet, woohyun, jpeg

Differential Revision: https://phab.enlightenment.org/D1917

Signed-off-by: Cedric BAIL <240633aa59d25638de9800ef43a88ad2e208d24d@osg.samsung.com>

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