Adapt condition in `SwitchProcessSequence` similar to !507
This MR adapts SwitchProcessSequence
similar to MR !507 (merged).
I encountered the problem that my very-high-energy EM showers (1e11 GeV) failed because SIBYLL got called with an electron as a projectile, which was exactly due to the zero-cross section case described in MR !507 (merged)