Removed an overzealous error message from ActionAtomistic

src/core/ActionAtomistic.cpp

@@ -51,7 +51,7 @@ donotforce(false),
 atoms(plumed.getAtoms())
 {
   atoms.add(this);
-  if(atoms.getNatoms()==0) error("Cannot perform calculations involving atoms without atoms");
+//  if(atoms.getNatoms()==0) error("Cannot perform calculations involving atoms without atoms");
 }
 
 void ActionAtomistic::registerKeywords( Keywords& keys ){