Properly extract channel variables for the SendFAX/ReceiveFAX Stasis messages

By the time something extracts the pointers from ast_json_pack, the channels
will already be disposed of. This patch properly pulls the information out of
the variables and packs them into the JSON blob.


git-svn-id: http://svn.asterisk.org/svn/asterisk/trunk@392607 f38db490-d61c-443f-a65b-d21fe96a405b