Missed a common case for needing to extend the buffer.

(closes issue #14716)
 Reported by: sum
 Patches: 
       20090402__bug14716.diff.txt uploaded by tilghman (license 14)
 Tested by: sum


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@186021 65c4cc65-6c06-0410-ace0-fbb531ad65f3