Old courses may never get backed up with automated backups

The code that determines if a course should be skipped during automated backups doesn't check if the course has ever been backed up. Use case:

• Make a course, set to invisible.
• Automated backups were not turned on until over a month later.
• Outcome: Automated backups skips the backup of that course.
• Expected: The course was backed up because it was never backed up via automated backups before. Next automated backup would skip this course.