set At also for meson projectile to avoid NaN

Processes/UrQMD/UrQMD.cc

@@ -92,9 +92,8 @@ corsika::process::EProcessReturn UrQMD::DoInteraction(SetupProjectile& projectil
     cascinit_(sys_.Zp, sys_.Ap, id);
   } else {
     inputs_.prspflg = 1;
-    int const Ap =
-        1; // what value to use here for non-baryons??? see CONEX UrQMD interface
-    rsys_.bdist = nucrad_(Ap) + nucrad_(Atarget) + 2 * options_.CTParam[30 - 1];
+    sys_.Ap = 1; // even for non-baryons this has to be set, see vanilla UrQMD.f
+    rsys_.bdist = nucrad_(sys_.Ap) + nucrad_(Atarget) + 2 * options_.CTParam[30 - 1];
 
     auto const [ityp, iso3] = ConvertToUrQMD(projectileCode);
     // todo: conversion of K_long/short into strong eigenstates;