With help from MageKing17: Fix for Mantis 3123: Virtual variables and indexers that return nil break the scripting system

git-svn-id: svn://svn.icculus.org/fs2open@11168 387891d4-d844-0410-90c0-e4c51a9137d3
Redo Coverity 1215458 Uninitialized pointer field

Includes more robust checks of cmdline_parm data

git-svn-id: svn://svn.icculus.org/fs2open@11169 387891d4-d844-0410-90c0-e4c51a9137d3