evas text: fix _ellipsis_get to return -1.0 on failure.

evas text: fix _ellipsis_get to return -1.0 on failure.

Summary:
When getting ellipsis value from evas text object fails,
the most reasonable return value is -1.0.
Currently, evas_object_text_ellipsis_get API with NULL returns 0.0.
It means ellipsis is not off. It must return -1.0 when API fails.
@fix

Comments by Tom: until now, this was inconsistent. With this change, it
now returns -1.0 consistently. Also, fixed commit summary.

Reviewers: woohyun, Hermet, seoz, tasn

Reviewed By: tasn

Subscribers: cedric

Differential Revision: https://phab.enlightenment.org/D1944