Developer credits
Git commits in Moodle 2.4.9 by Andrew Davis
commit 7748e17207b1a28118d9dc622878da22f956d3fe Author: Andrew Davis <andrew@moodle.com> Date: Mon, 03 Mar 2014 12:15:54 +0800 Tag: v2.4.9 MDL-44082 mod_chat: added a security check for users already in the chat activity