pjsip/dialplan_functions: Use the right buffer length when printing URIs

While entertaining, sizeof(buflen) is not the same as buflen. Doh.
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Merged revisions 403823 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: http://svn.asterisk.org/svn/asterisk/trunk@403824 f38db490-d61c-443f-a65b-d21fe96a405b