Explicitly set args in park_call_exec NULL so in the case of no options being passed in, there

 is no garbage attempted to be used. Also, do not set args to unknown value again if there are
 no options passed in.



git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@146875 65c4cc65-6c06-0410-ace0-fbb531ad65f3