Cycles: different fix for perlin noise generating nan values, now check for
the result to be finite afterwards which is a bit faster and works for OSL
too without needing to slow down OSL itself.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@53689 954f8c5b-7b00-dc11-b283-0030488c597c