fix page error on submissions endpoints

fixes CNVS-15298

test plan:
  - Get the /submissions/:id endpoint of any assignment preview
  - Logout of Canvas or use a different browser or use an
    incognito window so that you are not authenticated
  - Try to navigate to the submission ID from Step 1
  - You should be redirected to login rather than getting an error

Change-Id: I78ff821d91cceb36acfffcb7f5f8fd179fd29705
Reviewed-on: https://gerrit.instructure.com/40683
Reviewed-by: Simon Williams <simon@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Caleb Guanzon <cguanzon@instructure.com>
Product-Review: Simon Williams <simon@instructure.com>