fix module sequence footer on locked discussion topic
fix module sequence footer on locked discussion topic

test plan:
 - create a discussion topic that unlocks in the future
 - add it to a module
 - ensure that a student who clicks on the locked topic
   module item gets to a page with the "Prev" / "Next"
   module item buttons on the bottom of the page

fixes CNVS-32512

Change-Id: Icabdba0e12561a4de9bcf1c657c6045f45b9a17b
Reviewed-on: https://gerrit.instructure.com/93162
Tested-by: Jenkins
Reviewed-by: Clay Diffrient <9dff2e5c98626d20d2848250c411e8009465bb87@instructure.com>
QA-Review: David Tan <6283e310a2278fc51bdc4fb5974f70dd9c3366b9@instructure.com>
Product-Review: Jeremy Stanley <b3f594e10a9edcf5413cf1190121d45078c62290@instructure.com>

instructure/canvas-lms,venturehive/canvas-lms,HotChalk/canvas-lms,grahamb/canvas-lms,venturehive/canvas-lms,grahamb/canvas-lms,venturehive/canvas-lms,djbender/canvas-lms,grahamb/canvas-lms,djbender/canvas-lms,SwinburneOnline/canvas-lms,instructure/canvas-lms,matematikk-mooc/canvas-lms,HotChalk/canvas-lms,matematikk-mooc/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,venturehive/canvas-lms,instructure/canvas-lms,djbender/canvas-lms,grahamb/canvas-lms,sfu/canvas-lms,matematikk-mooc/canvas-lms,HotChalk/canvas-lms,matematikk-mooc/canvas-lms,djbender/canvas-lms,SwinburneOnline/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,HotChalk/canvas-lms,sfu/canvas-lms,SwinburneOnline/canvas-lms,instructure/canvas-lms,SwinburneOnline/canvas-lms,grahamb/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,instructure/canvas-lms