This change prevents a crash from occurring if res_musiconhold.so

is unloaded and then Asterisk is stopped. The problem was that
we are not unregistering the ast_moh_destroy function at exit.

(closes issue #13761)
Reported by: eliel
Patches:
      res_musiconhold.c.patch uploaded by eliel (license 64)



git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@157592 65c4cc65-6c06-0410-ace0-fbb531ad65f3