fixed some potentially problematic naming of blender stuff in the importer

git-svn-id: https://svn.blender.org/svnroot/bf-extensions/trunk/py/scripts/addons@4623 96b784f8-4ae3-dd11-aff7-0030488c597c
fix: previous commit (if load_image() returns an NoneObject)

git-svn-id: https://svn.blender.org/svnroot/bf-extensions/trunk/py/scripts/addons@4624 96b784f8-4ae3-dd11-aff7-0030488c597c