Lock around variables retrieved, and copy the values, if they stay persistent,

since another thread could remove them.
(closes issue #12541)
 Reported by: snuffy
 Patches: 
       bug_12156_apps.diff uploaded by snuffy (license 35)
       Several additional changes by me


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@114904 65c4cc65-6c06-0410-ace0-fbb531ad65f3