Fix typo: loop index was wrong

In principle, a serious bug: but for dimworld=3d (i.e., the standard)
this loop was never executed anyway.  Hence there were no serious
consequences.

dune/gfe/surfacecosseratenergy.hh

@@ -446,7 +446,7 @@ RT energy(const typename Basis::LocalView& localView,
       {
         for (int j=0; j<dimworld; j++)
           aCovariant[i][j] = jacobianTransposed[i][j];
-        for (int j=dimworld; j<3; i++)
+        for (int j=dimworld; j<3; j++)
           aCovariant[i][j] = 0.0;
       }