FreeSWITCH-FS-6836

Merge pull request #448 in FS/freeswitch from bugfix/FS-7911-master to master

* commit 'f2514644e1b9964bc4a2f91b8cbe6f8aedf1214b':
  FS-7911: [mod_conference] do not allocate for conference cdr if conference cdr is disabled, and fix leak in conference_record