Properly handles a None camera value if given.  Result will end up just being a negative return value.
Properly handles a None camera value if given.  Result will end up just being a negative return value.

git-svn-id: a3b746cc1383a42926249ed33eaccad697259b1b@16860 896c8824-d3f5-0310-9c61-ac502b9a79dc

blurstudio/cross3d