Blocked revisions 405350

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PJSIP: Backport r405270 - Unhold on reinvite without SDP

Adds behavior to unhold on a reinvite without an SDP section
Review: https://reviewboard.asterisk.org/r/3106/


git-svn-id: http://svn.asterisk.org/svn/asterisk/trunk@405351 f38db490-d61c-443f-a65b-d21fe96a405b