Actually check the "sendtodialplan" option setting for xmpp.

(closes issue ASTERISK-17978)
Reported by: elguero
Patches:
    stop_messages_going_to_dialplan.patch (license #5026)


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@322244 65c4cc65-6c06-0410-ace0-fbb531ad65f3