remove redundant NULL checks


git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@60619 954f8c5b-7b00-dc11-b283-0030488c597c
code cleanup: redundant includes and add minor comments.


git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@60620 954f8c5b-7b00-dc11-b283-0030488c597c