-fix NPE in NAT test

git-svn-id: https://gnunet.org/svn/gnunet@34327 140774ce-b5e7-0310-ab8b-a85725594a96
-fix format string

git-svn-id: https://gnunet.org/svn/gnunet@34328 140774ce-b5e7-0310-ab8b-a85725594a96
-return non-NULL even if we instantly fail

git-svn-id: https://gnunet.org/svn/gnunet@34329 140774ce-b5e7-0310-ab8b-a85725594a96