turnitin: don't crash if we don't get a status back
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 <d95b56ce41a2e1ac4cecdd398defd7414407cc08@instructure.com>
Reviewed-by: Liz Abinante <ce3305c9be70e1a5a9ff49df19e1a5b24d5a47f8@instructure.com>
QA-Review: Anna Koalenz <8df3af669343a6e717fd7441a9deea414b21645f@instructure.com>
Product-Review: Simon Williams <088e16a1019277b15d58faf0541e11910eb756f6@instructure.com>

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