avoid divide by zero on zero point assignments; fixes #10472
avoid divide by zero on zero point assignments; fixes #10472

Change-Id: If4f68dfec6bb1152f1c590d329912e1b56bd4676
Reviewed-on: https://gerrit.instructure.com/13621
Tested-by: Jenkins <d95b56ce41a2e1ac4cecdd398defd7414407cc08@instructure.com>
Reviewed-by: Jeremy Stanley <b3f594e10a9edcf5413cf1190121d45078c62290@instructure.com>

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