elm_label: Fixed to prevent slide's autostart before calling elm_label_slide_go()

elm_label: Fixed to prevent slide's autostart before calling elm_label_slide_go()

Summary:
Label should not start sliding before elm_label_slide_go() is called.
However, label starts sliding automatically,
because resize callback emits slide start signal.
This patch prevents label from sliding before calling elm_label_slide_go().

@fix

Reviewers: woohyun, Hermet, seoz

Subscribers: CHAN, woohyun

Differential Revision: https://phab.enlightenment.org/D1906