Corrected the problem of unnecessary clipping when using the PointPerspective...

Corrected the problem of unnecessary clipping when using the PointPerspective projection.  Fixes #3879

git-svn-id: http://subversion.wr.usgs.gov/repos/prog/isis3/trunk@7285 41f8697f-d340-4b68-9986-7bafba869bb8