do not show 0 points for moderated quizzes
do not show 0 points for moderated quizzes

fixes QO-523
flag = none

test plan:
 - create/publish a classic quiz
 - go to moderate the quiz
 - adding extra time/attempts for a student should
   not update the score column to a 0
 - actually scoring 0 on a quiz should show correctly

Change-Id: I6fb93db7bca94c22339d44a5247cbb71f09e1053
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/233358
Tested-by: Service Cloud Jenkins <9144042a601061f88f1e1d7a1753ea3e2972119d@instructure.com>
Reviewed-by: Syed Hussain <1379c89cd1d253d3c5a299cc4d8f6002ada9d6b5@instructure.com>
Reviewed-by: Jim Simon <801be5e70e868c2755b908d78d4b55d1f02ffb8c@instructure.com>
QA-Review: David Tan <6283e310a2278fc51bdc4fb5974f70dd9c3366b9@instructure.com>
Product-Review: Kevin Dougherty <d976013e3ceb631f24c072156980cd9ccba4cf84@instructure.com>

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