Fix missing initialisation of constants for event generation.
Bugfix mentioned in my presentation in simulation meeting on 12th May (https://indico.cern.ch/event/875990/contributions/3861648/attachments/2036833/3410501/evtGenChanges12May2020.pdf).
Bugfix mentioned in my presentation in simulation meeting on 12th May (https://indico.cern.ch/event/875990/contributions/3861648/attachments/2036833/3410501/evtGenChanges12May2020.pdf).