Blender Git Loki

EEVEE DoF: Fix runtime error: division by zero when blades was 0

Even though the fragment shader was already discarding all members of
dof_bokeh_sides when blades was zero, the C code was still trying to
use this for a few divisions leading to runtime asserts.

Those are harmless yet can lead some to waste time while pursuiting
other bugs (namely a near freeze when blades aspect ratio is too low).