This commit fixes a issue that could happen in case of user-defined event generators that attempt to directly add tracks via the

virtual void AddTrack(Int_t pdgid, Double_t px, Double_t py, Double_t pz,
                        Double_t vx, Double_t vy, Double_t vz,
                        Int_t parent = -1, Bool_t wanttracking = true,
                        Double_t e = -9e9, Double_t tof = 0.,
                        Double_t weight = 0., TMCProcess proc = kPPrimary);

method and do not specify a valid energy, that is they use the default.

For the cases where a negative energy is passed, a protection must be taken in the method to convert the negative value to a reasonable value. If the particle PDG id is known, than the mass is retrieved and the energy computed. Otherwise zero mass is assumed.