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).