avoid double render on deleted assessment question attachments

Change-Id: I7ee57d7fad459b36d93591676f34e902899dff08
Reviewed-on: https://gerrit.instructure.com/28229
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Anthus Williams <awilliams@instructure.com>
QA-Review: Cody Cutrer <cody@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>