Add missing handling for ringing state for use with queue empty options.

(closes issue #17471)
Reported by: jazzy
Patches: 
      app_queue.c.diff uploaded by jazzy (license 1056)


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@277366 65c4cc65-6c06-0410-ace0-fbb531ad65f3