ARI: Fix a crash caused by hanging during playback to a channel in a bridge

ASTERISK-24147 #close
Reported by: Edvin Vidmar
Review: https://reviewboard.asterisk.org/r/3908/
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Merged revisions 421879 from http://svn.asterisk.org/svn/asterisk/branches/12
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Merged revisions 421880 from http://svn.asterisk.org/svn/asterisk/branches/13


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@421881 65c4cc65-6c06-0410-ace0-fbb531ad65f3