fix roster user partial rendering

test plan:
  - make a discussion topic
  - as a student make a comment on it
  - go to users/:id_of_student_who_commented
  - under Recent Messages the comment in the
    discussion topic properly renders

Change-Id: Ib8dbf96690846987e6183b75580d7c90c54a1191
Reviewed-on: https://gerrit.instructure.com/43596
Reviewed-by: Cameron Sutter <csutter@instructure.com>
Product-Review: Simon Williams <simon@instructure.com>
QA-Review: Sean Lewis <slewis@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>