Ignore nuclei isospin only if equal to 9.

Author: pzhristov

Generators/src/GeneratorPythia8.cxx

@@ -654,14 +654,12 @@ Bool_t
     // first particle is system
     auto particle = event[iparticle];
     auto pdg = particle.id();
-#if PYTHIA_VERSION_INTEGER >= 8313
     // Select nuclei (A PDG id code for nuclei is on the form 100ZZZAAAI)
     if (std::abs(pdg) > 1000000000) {
-      // Ignore isospin
-      pdg /= 10;
-      pdg *= 10;
+      // Ignore isospin if equal to 9
+      auto pdgNoI = (pdg/10)*10;
+      if (std::abs(pdg-pdgNoI) == 9) pdg=pdgNoI;
     }
-#endif
     auto st = o2::mcgenstatus::MCGenStatusEncoding(particle.statusHepMC(), //
                                                    particle.status())      //
                 .fullEncoding;