Prevent double closing of FDs by EIVR

This caused a problem when asterisk was under heavy load and running both AGI and EIVR applications.
EIVR would close an FD at which point it would be considered freed and be used by a new AGI instance
the second close would then close the FD now in use by AGI.

(closes issue #16305)
Reported by: diLLec
Tested by: thedavidfactor, diLLec

Review: https://reviewboard.asterisk.org/r/436/


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@232587 65c4cc65-6c06-0410-ace0-fbb531ad65f3