fix null sorting of grading standards title

refs CNVS-3072

Change-Id: I7b34832c9486f7581dfa59e3e8223ef4676faad4
Reviewed-on: https://gerrit.instructure.com/28654
Reviewed-by: Anthus Williams <awilliams@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Cody Cutrer <cody@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>