Permit message wrap-around during message retrieval.

(closes issue #12254)
 Reported by: andrew
 Patches: 
       bug-12253.diff uploaded by snuffy (license 35)


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@113731 65c4cc65-6c06-0410-ace0-fbb531ad65f3