Fix issue where changing the volume of both directions of audio did not work.

(closes issue #14574)
Reported by: KNK
Patches:
      audiohook_volume_fix.diff uploaded by KNK (license 545)


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@179291 65c4cc65-6c06-0410-ace0-fbb531ad65f3