Blender Git Loki

Particles: don't output nonsense UV data for Grid distribution particles.

As reported in T48928, From Dupli UV is not supported for grid
distribution, and running the normal code as usual simply produces
nonsense data, because fuv is used to hold orco instead of
interpolation factors for uv, and num is zero.

Since support won't be added in 2.78, just stop outputting nonsense.