evas_textblock: prevent updating cursor unless they are ready during markup_set

Summary:
During Markup_set at text block level, we will not update the cursors, unless their status is updated and ready.

This can cause serious issues, especially if a cursor also depends on another cursor for some calculations, (like the segfault happening in TextBox T8637)

Reviewers: woohyun, bu5hm4n, zmike

Reviewed By: woohyun

Subscribers: cedric, reviewers, committers

Tags: efl

Maniphest Tasks: T8637

Differential Revision: https://phab.enlightenment.org/D11598