evas: Fix very unlikely crash in evas render

evas: Fix very unlikely crash in evas render

During a stress test of EFL a seemingly impossible crash happened, where
one of object's cow fields was NULL inside evas_object_was_visible.
Nothing in the code flow can possibly lead to this situation but
it still happened. For information, the object's delete_me flag was 2 in
evas_object_is_active() called from _evas_render_phase1_object_process().
So let's add a small safety check for crash prevention.

Differential Revision: https://phab.enlightenment.org/D4608