Bug fixes

One of our data migration scripts was inserting duplicate rows for guest purchasers in `email_contact`. This was a regression from 4.15.0.

We fixed a fault in the importer sync that occurred if the cron schedule for contact sync was set to ‘Every 60 Minutes’.

We fixed a bug with the catalog reset that happens when image type values are changed, in Dotdigital > Configuration > Image Types.

Some stored image types values could cause a blank screen in Dotdigital > Configuration; this has been fixed.