fix div by zero


git-svn-id: https://gnunet.org/svn/gnunet@30934 140774ce-b5e7-0310-ab8b-a85725594a96
- fix


git-svn-id: https://gnunet.org/svn/gnunet@30935 140774ce-b5e7-0310-ab8b-a85725594a96