Blender Git Loki

Fix T41538: Sun Beam Node has artifact at its radius.

The sunbeams node was clamping the range of influence to start at 1
pixel distance from the source. This was a poor fix for artifacts caused
by an off set in buffer coordinates. Since the u coordinate starts at
ceil(umax) the v coordinate also has to use ceil. This also fixes some
discontinuities that became visible when the source point is close to
a sharp line in the input image.