Git commits in Moodle 3.8.x by Johan Dobbelstein

commit 5b39bf184d49551b8de80e8934886a07f1cec74c
Author: Johan Dobbelstein <johan.dobbelstein@script.univ-paris-diderot.fr>
Date:   Mon, 02 Sep 2019 23:30:46 +0800
Tag:    v3.8.0-beta

MDL-66582 auth: Fix empty auth_logo in CAS/Shibboleth auth plugins