Git commits in Moodle 3.1.6 by Ruslan Kabalin

commit 231a80c01048292e833359d795497d8a37f2879b
Author: Ruslan Kabalin <r.kabalin@lancaster.ac.uk>
Date:   Fri, 07 Apr 2017 18:57:35 +0800
Tag:    v3.1.6

MDL-58539 assignfeedback_editpdf: Fix group assignment fatal error.