fix bug where essay questions answers not saved

closes CNVS-11603

test plan:
  - as an instructor
    - create and publish a quiz that:
      - has an essay question
      - has a time limit
      - allows students to see their submitted answers
  - as a student
    - start quiz
    - enter something via the RCE for the essay question (dont submit)
    - allow time to expire on the quiz
    - click 'Ok, fine' in the 'Times up' modal dialog that pops up
  - your answer should be displayed in the following quiz summary page

Change-Id: I0f8bc7ff177f3cd012ec8311fad631ec2f519348
Reviewed-on: https://gerrit.instructure.com/31403
Reviewed-by: Derek DeVries <ddevries@instructure.com>
QA-Review: Myller de Araujo <myller@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
Product-Review: Derek DeVries <ddevries@instructure.com>