Active Ci::PipelineSchedule have a nullified `next_run_at`

Summary

It turned out that a few Ci::PipelineSchedule exists with active = true and next_run_at IS NULL (See https://gitlab.com/gitlab-com/infrastructure/issues/2396#note_36518030).

This should not happen.

We should figure out why this happened and add a new patch to rescue those cases.

Steps to reproduce

WANTED!!!!!!!

What is the current bug behavior?

Some pipeline_schedules are active but next_run_at is nil.

What is the expected correct behavior?

All active pipeline_schedules must have next_run_at.

Output of checks

This bug happens on GitLab.com

Possible fixes

WANTED!!!

Links

• ZD: https://gitlab.zendesk.com/agent/tickets/80289
• https://gitlab.com/gitlab-org/gitlab-ce/issues/32790#note_36353999
• https://gitlab.com/gitlab-com/infrastructure/issues/2396#note_36518030

Important

A patch which added at https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/13286 should be removed after we've figured out this culprit. https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/13286#note_36745307

/cc @zj @ayufan