Fix race condition with doc loading in quizzes
Fix race condition with doc loading in quizzes

Closes MAT-638
flag=none

Test Plan:
1. Navigate to /courses/:id/question_banks and add
   a new question bank
2. Add a multiple choice question to the bank and save
   some bogus data
3. Hard refresh the page
4. Edit the multiple choice question
5. Hover your mouse over one of the answers and click the
   pencil icon
6. Verify the RCE loads
7. Repeat steps 3 - 6 a few times. Make sure the RCE loads
   each time. This is obviously not exaustive :)
8. Verify you can save changes to answers

Change-Id: I9a306ce7d3334ed691c108bffa33d8e81e287e63
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/285692
Reviewed-by: Joe Hernandez <2475ff9f2214a383ad29b079daec0de5f5df5945@instructure.com>
QA-Review: Joe Hernandez <2475ff9f2214a383ad29b079daec0de5f5df5945@instructure.com>
Product-Review: Weston Dransfield <e9203059795dc94e28a8831c65eb7869e818825e@instructure.com>
Tested-by: Service Cloud Jenkins <9144042a601061f88f1e1d7a1753ea3e2972119d@instructure.com>

sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms