print notice when guest views chat.

lang/en/chat.php

@@ -35,6 +35,7 @@ $string['modulename'] = 'Chat';
 $string['modulenameplural'] = 'Chats';
 $string['neverdeletemessages'] = 'Never delete messages';
 $string['nextsession'] = 'Next scheduled session';
+$string['noguests'] = 'The chat is not open to guests';
 $string['nomessages'] = 'No messages yet';
 $string['repeatdaily'] = 'At the same time every day';
 $string['repeatnone'] = 'No repeats - publish the specified time only';

mod/chat/view.php

@@ -102,6 +102,8 @@
         link_to_popup_window ("/mod/chat/gui_$CFG->chat_method/index.php?id=$chat->id$groupparam", 
                               "chat$course->id$chat->id$groupparam", "$strenterchat", 500, 700, $strchat);
         print_simple_box_end();
+    } else {
+        notice(get_string('noguests', 'chat'));
     }