Fix add ticket button when "ticket_allow_student_add" setting is on

BT#13392

main/ticket/tickets.php

@@ -228,7 +228,8 @@ if (!empty($projectId)) {
         )
     );
 
-    if (api_is_platform_admin()) {
+    // Add link
+    if (api_get_setting('ticket_allow_student_add') == 'true' || api_is_platform_admin()) {
         $actionRight = Display::url(
             Display::return_icon(
                 'add.png',
@@ -239,7 +240,9 @@ if (!empty($projectId)) {
             api_get_path(WEB_CODE_PATH) . 'ticket/new_ticket.php?project_id=' . $projectId,
             ['title' => get_lang('Add')]
         );
+    }
 
+    if (api_is_platform_admin()) {
         $actionRight .= Display::url(
             Display::return_icon(
                 'export_excel.png',