Very small change. A little performance for cron if admin enabled sending email for...

Very small change. A little performance for cron if admin enabled sending email for pending orders expiring.

1- If dailysettlement is 00:05 and cron executes at this time, nothing will occur. If it is executes at 00:10 it works. I think "<" works faster then "<=" :))
2- Don't compare course->ids by authorize->courseid, because courses are grouped by courseid. We sure each line is unique.
3- Only get pendingorderexpiring strings for sending email if course teachers exist.

Merged from 16stable.