Users with a role containing the "administer chats" permission can't chat !

In this case, the POST to chatroomread.php is incomplete, instead of something like
message=foo&anonName=&formToken=528d22e8da6bfba78d181502d05e22be&formId=chatroom_chat_buttons
it contains only
message=foo

To reproduce the bug
- create a new role
- give the ""administer chats" perm to it
- give the "chat access" perm to authenticated users
- attrib the role to a user
- create a new chat
- log in with this user
- try to chat...