Don't leak memory if phoneprov.conf does not exist

(closes issue #14203)
Reported by: jamesgolovich
Patches: 
      asterisk-phoneprovleak.diff.txt uploaded by jamesgolovich (license 176)


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@168142 65c4cc65-6c06-0410-ace0-fbb531ad65f3