Sorting by Average Progress filters out any courses with 0% completion

[brianhogg]

Reproduction Steps

1. Go to LifterLMS > Reporting > Courses, ensure there's a course with 0% progress and a course with > 0%
2. Click on the "Average Progress" header to sort by average progress

Expected Behavior

Courses are sorted by average progress with 0% progress on the bottom (or top, depending on direction)

Actual Behavior

Courses with 0% average progress are removed from the table

This issue has be recreated:

• Locally
• On a staging site
• On a production website
• With only LifterLMS and a default theme