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)

corsika/detail/framework/process/SwitchProcessSequence.inl

@@ -403,7 +403,7 @@ namespace corsika {
         }
 
         // check if we should execute THIS process and then EXIT
-        if (cx_select <= cx_sum) {
+        if (cx_select < cx_sum) {
 
           if constexpr (has_signature_cx1) {