chan_misdn: Fix sending RELEASE_COMPLETE in response to SETUP.

chan_misdn: Fix sending RELEASE_COMPLETE in response to SETUP.

Fix sending a RELEASE_COMPLETE in response to a SETUP if chan_misdn does
not have a B channel available to assign to the call.

(closes issue ABE-2869)
Reported by: Guenther Kelleter
Patches:
      setup-reject_2.diff (license #6372) patch uploaded by Guenther Kelleter
      Modified

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Merged revision 376949 from https://origsvn.digium.com/svn/asterisk/be/branches/C.3-bier
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Merged revisions 376950 from http://svn.asterisk.org/svn/asterisk/branches/1.8

git-svn-id: https://origsvn.digium.com/svn/asterisk/certified/branches/1.8.15@376955 65c4cc65-6c06-0410-ace0-fbb531ad65f3