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: http://svn.asterisk.org/svn/asterisk/trunk@399696 f38db490-d61c-443f-a65b-d21fe96a405b