fix quiz question parsing for non-eager loading

fixes CNVS-13791

with non-eagerloading, the constants might not be present, so we just
have to try to get it, instead of checking if we have it

test plan:
 * in development mode, make sure cache_classes is false
 * create a quiz with a fill in multiple answers question
 * save it
 * preview the quiz
 * it should not page error

Change-Id: Iacdebd972e4b0d6f404e8f0a6a91a8adecb77ca8
Reviewed-on: https://gerrit.instructure.com/37172
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Ahmad Amireh <ahmad@instructure.com>
QA-Review: Caleb Guanzon <cguanzon@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>