Fix a memory leak in chan_oss

(closes issue #13311)
Reported by: eliel
Patches:
      chan_oss.c.patch uploaded by eliel (license 64)



git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@141995 65c4cc65-6c06-0410-ace0-fbb531ad65f3