res_pjsip_pubsub: Set the body generation result to 0 for a valid path

The result of the "ast_sip_pubsub_generate_body_content" was not
set/initialized.  Consequently, the nominal path potentially returned
an invalid value, thus not sending mwi notifications.


git-svn-id: http://svn.asterisk.org/svn/asterisk/branches/12@412074 f38db490-d61c-443f-a65b-d21fe96a405b