Fix file playback in many cases.

(closes issue #12115)
Reported by: pj
Patches:
      v2-fileexists.patch uploaded by dimas (license 88) (with modifications by me)
Tested by: dimas, qwell, russell


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@106439 65c4cc65-6c06-0410-ace0-fbb531ad65f3