turnitin: don't crash if we don't get a status back

fixes CNVS-15440

test plan:
- submitting to turnitin still works

Change-Id: I6fafbc784908a883bf1511112b88c57b8f4c9d5d
Reviewed-on: https://gerrit.instructure.com/40935
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Liz Abinante <labinante@instructure.com>
QA-Review: Anna Koalenz <akoalenz@instructure.com>
Product-Review: Simon Williams <simon@instructure.com>