Blender Git Loki

Fix T68542: ParticleSystem.uv_on_emitter returns always 0,0 while Particle.uv_on_emitter returns a value.

'cached' particles (for paths actually) are only generated for some kind
(hair, keyed, and baked system afaik), not for all.

Note that we could probably just use directly `totpart` and `totchild`,
but keeping code as close to what it was as possible, for now...