Followup to rB3834dc2f7b38 (where getting the proper particle system was
fixed for the Adjust Last Operation panel in the Properties Editor). But
since this operator can also be called from the 3DView, get a current
particle system there as well.

Without this, _all_ particle systems would be copied when executing from
the 3DView (which was never really intended [operator description uses
singular] -- it just happens to use copy_particle_systems_to_object
internally as well -- same as the Copy Active/All to Selected Objects
operators)).

ref. T83317