Remove N+1 on UserMailer#send_daily_triage
Remove N+1 on UserMailer#send_daily_triage

When UserMailer render the emails, the view have a N+1 since
it is trying to get properties from issue, user and repo relations
on the loop of assignments.

Also:

- removing an extra assigment on the @assigments ivar
- moving the set_and_check_user guard before performing the query

codetriage/codetriage,codetriage/codetriage,codetriage/codetriage