Change test for valid geometry at a line/sample in phocube to check return...

Change test for valid geometry at a line/sample in phocube to check return result of Camera method rather than state of the shape model. Fixes #2252.

git-svn-id: http://subversion.wr.usgs.gov/repos/prog/isis3/trunk@6192 41f8697f-d340-4b68-9986-7bafba869bb8