Git commits in Moodle 3.3.x by Carlos Alexandre S. da Fonseca

commit d36fdb9657fc17344e61b4f18fbf6104257c0e49
Author: Carlos Alexandre S. da Fonseca <bozohhot@hotmail.com>
Date:   Tue, 21 Nov 2017 20:26:39 +0800
Tag:    v3.3.4

MDL-24678 mod_chat: Fixed race condition on chat module