Code cleanup: fix some vs2012 compiler warnings

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@57633 954f8c5b-7b00-dc11-b283-0030488c597c
Fix #35804: NVidia OpenCL render issue after sampler changes, workaround what looks like a compiler bug.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@57634 954f8c5b-7b00-dc11-b283-0030488c597c