fix blueprint history with syllabus sync
fix blueprint history with syllabus sync

sync exceptions due to downstream changes work just fine.
but history won't load if there are _no_ exceptions. :facepalm:

test plan:
 - have a blueprint course syncing to associated courses
 - change the syllabus body in the blueprint (and not in any
   of the associated courses, so the change goes to all of them)
 - ensure the sync history loads

fixes ADMIN-1346

Change-Id: I85cd22d072b3ec87b2831b5410a00d098d2d23ba
Reviewed-on: https://gerrit.instructure.com/162664
Reviewed-by: James Williams  <3a5f4ed991dbfa5c9ef76ad729d240ca12f62180@instructure.com>
Tested-by: Jenkins
QA-Review: Carl Kibler <7c2b40129dd885a147d5b2dda56dda016b9a8f57@instructure.com>
Product-Review: Jeremy Stanley <b3f594e10a9edcf5413cf1190121d45078c62290@instructure.com>

sfu/canvas-lms,djbender/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,djbender/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,djbender/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,djbender/canvas-lms