fixes #1297 check output buffer before cleaning it

action.php

@@ -221,8 +221,12 @@ if (ini_get('safe_mode') == 0)
   @set_time_limit(0);
 }
 // Without clean and flush there may be some image download problems, or image can be corrupted after download
-ob_clean();
-flush();
+if (ob_get_length() !== FALSE)
+{
+  ob_clean();
+  flush();
+}
+
 @readfile($file);
 
 ?>