Author: Simon Mok
MDL-68070 messaging: Fix error when personal notification is disabled
http://git.moodle.org/gw?p=moodle.git;a=commit;h=6de6fe9590fecff5ec478f007fe9150790dd2c03
http://github.com/moodle/moodle/commit/6de6fe9590fecff5ec478f007fe9150790dd2c03
+ 3.9 en [messageundeliveredbynotificationsettings,core_error]