Don't fast forward past the end of a message.

Don't fast forward past the end of a message.

This is nice change for users of the voicemail application.  If someone gets a
little carried away with fast forwarding through a message, they can easily
get to the end and accidentally exit the voicemail application by hitting the
fast forward key during the following prompt.

This adds some safety by not allowing a fast forward past the end of a message.

(closes issue #14554)
Reported by: lacoursj
Patches:
      21761.patch uploaded by lacoursj (license 707)
Tested by: lacoursj

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.4@203785 65c4cc65-6c06-0410-ace0-fbb531ad65f3