FourVector eta is missing protection for a particle along the beam/z axis

Hi there,

This concerns HepMC3, not HepMC2, and I am not sure which project this should be in.

I have seen floating point exceptions in !64960 due to the eta calculation of FourVector in HepMC3 for particles going along the z-axis.

I think that one needs to check that the three vector is not along z axis which results in division by zero or log of zero. This is protected in HepMC2 but not HepMC2.

eta

For comparison: 

HepMC3:  eta, and 
HepMC2: pseudoRapidity

see you, RD