Merge branch 'cherry-pick-5c99a242baf-21.9' into '21.9'

Sweeping !46581 from master to 21.9.
GeneratorObjectsTPCnv: Clear flow information when reading.

See merge request atlas/athena!46613

Generators/GeneratorObjectsTPCnv/src/McEventCollectionCnv_p2.cxx

@@ -245,6 +245,7 @@ McEventCollectionCnv_p2::createGenParticle( const GenParticle_p2& persPart,
 
   // fillin' the flow
   const unsigned int nFlow = persPart.m_flow.size();
+  p->m_flow.clear();
   for ( unsigned int iFlow= 0; iFlow != nFlow; ++iFlow ) {
     p->m_flow.set_icode( persPart.m_flow[iFlow].first,
                          persPart.m_flow[iFlow].second );

Generators/GeneratorObjectsTPCnv/src/McEventCollectionCnv_p3.cxx

@@ -277,6 +277,7 @@ McEventCollectionCnv_p3::createGenParticle( const GenParticle_p3& persPart,
 
   // setup flow
   const unsigned int nFlow = persPart.m_flow.size();
+  p->m_flow.clear();
   for ( unsigned int iFlow= 0; iFlow != nFlow; ++iFlow ) {
     p->m_flow.set_icode( persPart.m_flow[iFlow].first,
                          persPart.m_flow[iFlow].second );

Generators/GeneratorObjectsTPCnv/src/McEventCollectionCnv_p4.cxx

@@ -403,6 +403,7 @@ McEventCollectionCnv_p4::createGenParticle( const GenParticle_p4& persPart,
 
   // setup flow
   const unsigned int nFlow = persPart.m_flow.size();
+  p->m_flow.clear();
   for ( unsigned int iFlow= 0; iFlow != nFlow; ++iFlow )
     {
       p->m_flow.set_icode( persPart.m_flow[iFlow].first,