Hepmc3 nightly fixes 09122020 part 1
This MR contains small fixes missed in the HepMC3 branch:
- Detection of HepMC3 in CmakeLists for the HepMC3 branch
- typo fix, . vs ->
- indentation in one case
- having
par_invariable out of the outside loop
This MR contains small fixes missed in the HepMC3 branch:
par_in variable out of the outside loop