Explicitely unset oldCritical in case the mmg is reused

dune/solvers/iterationsteps/mmgstep.hh

@@ -43,6 +43,7 @@ public:
     {
         Base::setProblem(mat,x,rhs);
         oldCritical.resize(x.size(), false);
+        oldCritical.unsetAll();
     }
 
     virtual void iterate();