fix bug reported by richard berger via...

fix bug reported by richard berger via https://ci.lammps.org/job/lammps/job/master/job/regression/160/testReport/junit/examples/msst/msst/

src/SHOCK/fix_msst.cpp

@@ -434,6 +434,7 @@ void FixMSST::setup(int vflag)
 
   // trigger virial computation on next timestep
 
+  pe->addstep(update->ntimestep+1);
   pressure->addstep(update->ntimestep+1);
 }