* Fix bug in filling the Beam initial condition

* x was filled instead of z

NPSimulation/src/ParticleStack.cc

@@ -109,7 +109,7 @@ void ParticleStack::AddBeamParticleToStack(Particle& particle){
   m_InitialConditions-> SetIncidentFinalKineticEnergy (particle. GetParticleKineticEnergy());
   m_InitialConditions-> SetIncidentPositionX     (particle. GetParticlePosition().x());
   m_InitialConditions-> SetIncidentPositionY     (particle. GetParticlePosition().y());
-  m_InitialConditions-> SetIncidentPositionZ     (particle. GetParticlePosition().x());
+  m_InitialConditions-> SetIncidentPositionZ     (particle. GetParticlePosition().z());
   
   m_First=false;
 }
@@ -248,4 +248,4 @@ void ParticleStack::ShootAllParticle(G4Event* anEvent){
   }
   m_ParticleStack.clear();
   m_First=true;
-}
\ No newline at end of file
+}