Author: Simon Mok
MDL-68070 messaging: Fix error when personal notification is disabled
http://git.moodle.org/gw?p=moodle.git;a=commit;h=af2a02e4606dcb2fd9c421a5f402f7ccef1e9b8b
http://github.com/moodle/moodle/commit/af2a02e4606dcb2fd9c421a5f402f7ccef1e9b8b
+ 3.8 en [messageundeliveredbynotificationsettings,core_error]