SpeedGrader intermittently caches previously saved question score
SpeedGrader intermittently caches previously saved question score

flag=none

closes QO-569

test plan:
- hard to test/reproduce
- create an old quiz with many questions (perhaps 35+)
- add more than 20 students to the quiz
- take the quiz with the 20 different students
- on speedgrader, update grade of the 1st question and
  navigate to the next submission
- follow test procedure in invetigation notes in QO-569
- also need a regression on speedgrader functionalities

Change-Id: I13fe660e06de46d6912a0832dd345cbb09654b25
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/229903
Tested-by: Service Cloud Jenkins <9144042a601061f88f1e1d7a1753ea3e2972119d@instructure.com>
QA-Review: David Tan <6283e310a2278fc51bdc4fb5974f70dd9c3366b9@instructure.com>
Product-Review: Kevin Dougherty <d976013e3ceb631f24c072156980cd9ccba4cf84@instructure.com>
Reviewed-by: Jared Crystal <06625ed3fabb97fffd807b5fd3c4e9314fe77676@instructure.com>

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