Added VerifyCube method to check for the existence of a camera or a projection...

Added VerifyCube method to check for the existence of a camera or a projection in a cube before entering the large try catch block, the real solution would be for Chip::Load to take a UniversalGroundMap.

git-svn-id: http://subversion.wr.usgs.gov/repos/prog/isis3/trunk@2143 41f8697f-d340-4b68-9986-7bafba869bb8