ecore_anim: Check for null ptr deref

Summary:
This patch fixes a tentative crash owing to null ptr dereference
ecore_animator_freeze() has a same patch already.

Test Plan: execute test suite

Reviewers: cedric, raster, jpeg, stefan, Jaehyun_Cho

Reviewed By: Jaehyun_Cho

Differential Revision: https://phab.enlightenment.org/D5752