org.ametys.odf.schedulable.CoursePartPurgeSchedulable calls solr to find all coursepart not linked to a course.

If there was an indexation problem, some coursepart can be deleted just because solr does not know their real state.

There are 2 ways of fixing this :

1. Instead of solr, query the repository (take care, it is possible to have an empty array or no value at all, both cases must be checked)
2. Continue to use solr, but check in the repository if the result is correct before deletion.

And some logs could be added.