Blender Git Loki

Fix T51774: Children particles hair interpolation not correct with textures or dp.

Children where always getting at least one segment of fixed length...

Now fully hidden ones (zero length) get no segment at all.

Note that even very short ones keep getting one 'unit' length segment - would
rather avoid changing that at this point, given how complex children
particles 'length' can get with all kind of modifiers... Think we can
live with that for now anyway.