Fix IMAP app_voicemail compilation issue introduced in r354429

This simply fixes the compilation issue introduced in r354429 by
re-adding the 'quote' variable.

(closes issue ASTERISK-19337)
Reported by: John Taylor


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@354799 65c4cc65-6c06-0410-ace0-fbb531ad65f3