Fixed issue with undoing the initial entity application
Fixed issue with undoing the initial entity application

Summary: If you pressed undo right at the beginning, it would undo the entities being applied

Test Plan: Make text with widgets, permalink, refresh, then press undo.  observe ntohing changing

Reviewers: emily

Reviewed By: emily

Subscribers: jared

Differential Revision: https://phabricator.khanacademy.org/D30284

ariabuckles/perseus,ariabuckles/perseus,ariabuckles/perseus,ariabuckles/perseus,learningequality/perseus,learningequality/perseus