Blender Git Loki

Fix T80900: Crash lasso-selecting in particle editmode in certain
situations

In the situation that the PTCacheEdit is not available (e.g. when
editing unbaked Cloth or Softbody caches - or, as in the report, being
in Cloth or Softbody Editing Type for Hair particles), accesing the
corresponding ParticleSystem or ParticleSystemModifierData would crash.

Now access these later (after PE_start_edit had the chance to return
early on this non-valid situation).

Reviewers: JacquesLucke

Maniphest Tasks: T80900

Differential Revision: https://developer.blender.org/D8941