res_pjsip_mwi: Subscribe fails when missing aor name

res_pjsip_mwi: Subscribe fails when missing aor name

When subscribing to MWI (res_pjsip_mwi) and the sip uri did not contain a name
(ex: sip:<ip address>) then the subscription would fail since it would be unable
to locate an associated aor.  This patch makes it so that when a subscribe comes
with no aor name then it will subscribe to all aors on the located endpoint.

(closes issue ASTERISK-23072)
Reported by: Bob M
Review: https://reviewboard.asterisk.org/r/3164/
........

Merged revisions 407014 from http://svn.asterisk.org/svn/asterisk/branches/12

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@407015 65c4cc65-6c06-0410-ace0-fbb531ad65f3