Export selected tickets shows blank popup and a 404 on ajax.php/export//check after upgrading to 1.18.3.

The file is being deleted before the browser can download it. In ajax.tickets.php, the queueExport() function deletes the temp file via @$exporter->delete(), but class.export.php's download() function already deletes it after sending. Comment out or remove the premature delete call in ajax.tickets.php and let download() handle cleanup. This is environment-dependent because Http::flush() / fastcgi_finish_request() buffering timing affects whether the file still exists when the client checks.