Fix a crash when a hair system's `ParticleSettings` ID datablock was
linked from another file but couldn't be found. This results in default
settings, with `type = PART_EMITTER`, where the particle data still has
a non-NULL `hair` pointer. Previously, copies of such a particle system
would NOT copy hair data for non-hair particle systems, hence the
pointer of the copy pointed to the original data, which got freed (at
least) twice upon closing the blend file.
This is now fixed by always copying the hair data, regardless of the
particle system type.
Reviewed by: mont29
Differential Revision: https://developer.blender.org/D13245
Sybren A. Stüvel
72ee62e0da