Prevent slow graceful shutdown when outbound publications never started.

Prevent slow graceful shutdown when outbound publications never started.

The code was missing the case for explicitly destroying an outbound publication
when Asterisk had never actually published anything. The result was that Asterisk
would hang for a while on a graceful shutdown.

With this change, the case is taken into account, and on a graceful shutdown, these
publications are destroyed without the need to actually send a PUBLISH request.

ASTERISK-24655 #close
Reported by Kevin Harwell

Review: https://reviewboard.asterisk.org/r/4325

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/13@430608 65c4cc65-6c06-0410-ace0-fbb531ad65f3