Git commits in Moodle 3.8.x by Simon Mok

commit af2a02e4606dcb2fd9c421a5f402f7ccef1e9b8b
Author: Simon Mok <simonmok@outlook.com>
Date:   Mon, 12 Oct 2020 19:33:18 +0800
Tag:    v3.8.6

MDL-68070 messaging: Fix error when personal notification is disabled