MDL-57569 core_files: Fix to let show generated f3 image

lib/filelib.php

@@ -4088,7 +4088,7 @@ function file_pluginfile($relativepath, $forcedownload, $preview = null, $offlin
         $filename = array_pop($args);
 
         if ($filearea === 'badgeimage') {
-            if ($filename !== 'f1' && $filename !== 'f2') {
+            if ($filename !== 'f1' && $filename !== 'f2' && $filename !== 'f3') {
                 send_file_not_found();
             }
             if (!$file = $fs->get_file($context->id, 'badges', 'badgeimage', $badge->id, '/', $filename.'.png')) {