Comment 1 for bug 1823983

This turns out to be a very straight-forward fix. Branch here:

https://git.evergreen-ils.org/?p=working/Evergreen.git;a=shortlog;h=refs/heads/user/miker/lp-1823983-keep_event_id_filter_on_delay_repeat_check

From the commit message:

This bug has existed since the repeat_delay feature was added, but likely only rarely was triggered because most events don't have a repeat_delay, and those that do don't interact with the same target. However, as more repeatable event definitions are created, inappropriate interaction becomes more likely.

In this commit we avoid overwriting the whole join condition clause, which already contains an event definition id filter and needs to retain it.

Included is an unrelated change that uses the new-ish form of interval_to_seconds that avoids DST boundary shifting issues by passing a context DateTime object as the second parameter.