fix issue with hidden regrade tour overlay blocking quiz edit links

fixes CNVS-16719

test plan:
  - as a teacher
    - create a quiz

  - as a student
    - take the quiz

  - as a teacher
    - edit the quiz
    - the left side navigation links should all be clickable
    - edit the question to change the answer and regrade
    - the regrade tour should appear
    - close the regrade tour
    - the hidden overlay should still not be blocking the navigation links

Change-Id: I656de5f08c7c5696ff9f8e202e3e869e529cf1b0
Reviewed-on: https://gerrit.instructure.com/44411
Reviewed-by: Jason Madsen <jmadsen@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Trevor deHaan <tdehaan@instructure.com>
Product-Review: Derek DeVries <ddevries@instructure.com>