Blender Git Loki

Fix T63788: Crash if particle system is turned off in particle editing mode

Make sure particle system edit never points to a modifier or particle system
which becomes inactive.

This is needed because copy-on-write will change pointers of them and those
pointers are supposed to be restored from particle system evaluation. But
since the particle system is disabled it never updates pointers.

Reviewers: brecht

Reviewed By: brecht

Differential Revision: https://developer.blender.org/D5180