Fix MARK ALL MESSAGES AS READ seen by guest

Signed-off-by: illori <illori@simplemachines.org>

Themes/default/BoardIndex.template.php

@@ -248,7 +248,7 @@ function template_main()
 		</ul>';
 
 	// Show the mark all as read button?
-	if (!$user_info['is_guest'] && !empty($context['categories']))
+	if ($settings['show_mark_read'] && !empty($context['categories']))
 	echo '
 		<div class="mark_read">', template_button_strip($context['mark_read_button'], 'right'), '</div>';
 }