Fix #35330: Blur node crash due to size overflow

Issue was caused by too hight value used for size,
which came from infinite Z-buffer point.

Solved the crash by clamoing maximal gaussian table
radius to 30K, which seems to be reasonable.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@56759 954f8c5b-7b00-dc11-b283-0030488c597c