Fix assignment of coordinates for XdmfRectilnearGrid

In conversion of vtkRectilinearGrid to XdmfRectilinearGrid,
vtkRectilinearGrid::XCoordinates should be set to XCoords of
XdmfRectilinearGrid and vtkRectilinearGrid::ZCoordinates should be
set to ZCoords of XdmfRectilinearGrid respectively.

Both XdmfRectilinearGrid and vtkRectilinearGrid use the topology that
X (or I) indices varies at first.

IO/Xdmf3/vtkXdmf3DataSet.cxx

@@ -1341,7 +1341,7 @@ void vtkXdmf3DataSet::VTKToXdmf(
 
   bool OK = true;
   vtkDataArray *vCoords = dataSet->GetXCoordinates();
-  OK &= vtkXdmf3DataSet::VTKToXdmfArray(vCoords, xZCoords.get());
+  OK &= vtkXdmf3DataSet::VTKToXdmfArray(vCoords, xXCoords.get());
   if (OK)
   {
     vCoords = dataSet->GetYCoordinates();
@@ -1349,7 +1349,7 @@ void vtkXdmf3DataSet::VTKToXdmf(
     if (OK)
     {
       vCoords = dataSet->GetZCoordinates();
-      OK &= vtkXdmf3DataSet::VTKToXdmfArray(vCoords, xXCoords.get());
+      OK &= vtkXdmf3DataSet::VTKToXdmfArray(vCoords, xZCoords.get());
     }
   }