app_queue: Don't be quite so aggressive in initializing the array

We only need the first character.
........

Merged revisions 399695 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@399696 65c4cc65-6c06-0410-ace0-fbb531ad65f3