Fix course_chat_restrict_to_coach - refs BT#13885

Tutors only can chat with students when course_chat_restrict_to_coach is enabled

main/inc/lib/CourseChatUtils.php

@@ -57,6 +57,10 @@ class CourseChatUtils
                     $criteria->andWhere(
                         Criteria::expr()->eq('status', Session::STUDENT)
                     );
+                } else {
+                    $criteria->andWhere(
+                        Criteria::expr()->eq('status', Session::COACH)
+                    );
                 }
             }