Fixed an error introduced in last change which caused grid to no longer work...

Fixed an error introduced in last change which caused grid to no longer work on multi-band cubes that don't have a camera model (such as mosaics). Fixed 4586.

git-svn-id: http://subversion.wr.usgs.gov/repos/prog/isis3/trunk@7426 41f8697f-d340-4b68-9986-7bafba869bb8