res_pjsip: Fix assertion for pjsip.conf authorization list options.

(closes issue ASTERISK-23168)
Reported by: George Joseph

Review: https://reviewboard.asterisk.org/r/3143/


git-svn-id: http://svn.asterisk.org/svn/asterisk/branches/12@407324 f38db490-d61c-443f-a65b-d21fe96a405b