edje: update a style when a style is added as class's member

edje: update a style when a style is added as class's member

Summary:
If there is no member styles when a text_class is updated,
newly added styles can't be updated.
So, newly added styles as member of text_class should be updated.
@fix

Test Plan:
Test case is included.

1. Run "elementary_test -to "font overlay""
2. Press Next button. Check the font size.
3. Press Prev button.
4. Put font_size as 50
5. Click Apply button.
6. Press Next button. Check the font size is not changed.

Reviewers: cedric, tasn, herdsman, raster

Subscribers: jpeg, z-wony, Blackmole

Differential Revision: https://phab.enlightenment.org/D4125