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/


git-svn-id: http://svn.asterisk.org/svn/asterisk/branches/12@421879 f38db490-d61c-443f-a65b-d21fe96a405b