Only re-add the io port if it was closed, otherwise reload causes a memory

leak.
(closes issue #13785)
 Reported by: eliel
 Patches: 
       chan_mgcp.c.patch uploaded by eliel (license 64)


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@152442 65c4cc65-6c06-0410-ace0-fbb531ad65f3