don't die if a deleted section is present in student.sections refs: #9249
don't die if a deleted section is present in student.sections
refs: #9249

Change-Id: I92adaac0a6a114e5841fd199c56def769d38f3d9
Reviewed-on: https://gerrit.instructure.com/11959
Tested-by: Jenkins <d95b56ce41a2e1ac4cecdd398defd7414407cc08@instructure.com>
Reviewed-by: Mark Ericksen <776ab05fc6b68e82d2b2c63873bf56edde131809@instructure.com>

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