opigno_learning_path_step_achievement records have completed = NULL when they're passed

Problem/Motivation

This is an infrequent bug (I found approx 40 records out of over 4,000 with the problem), but when you run into it, it results in users who have completed courses being unable to download certificates and similar issues.

opigno_learning_path_save_step_achievements() clearly has logic to set the completed timestamp to null, presumably when a step isn't passed yet, but sometimes the step is passed and it ends up as null anyway.

Steps to reproduce

No steps to reproduce yet - we found this by examining data in the table.

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes

Release notes snippet