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/
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Merged revisions 407324 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@407325 65c4cc65-6c06-0410-ace0-fbb531ad65f3