handle user loaded notification_policy_overrides
handle user loaded notification_policy_overrides

this is the same functionality as before but avoids the query when they
are already loaded.

test plan
 - specs should pass

refs VICE-1280
flag = none

Change-Id: I20e711b222874f9d082c6a4a284b7a1b4346193b
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/263268
Tested-by: Service Cloud Jenkins <9144042a601061f88f1e1d7a1753ea3e2972119d@instructure.com>
Reviewed-by: Matthew Lemon <7bd6faf60934a850234395b3b97cb1fc9250fa11@instructure.com>
QA-Review: Matthew Lemon <7bd6faf60934a850234395b3b97cb1fc9250fa11@instructure.com>
Product-Review: Matthew Lemon <7bd6faf60934a850234395b3b97cb1fc9250fa11@instructure.com>

sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms