Fix vtkPolyData Reset

Reset should delete the Links and Cells objects so that they can be rebuilt
when needed.

Common/DataModel/vtkPolyData.cxx

@@ -1390,6 +1390,10 @@ void vtkPolyData::Reset()
     {
     this->Strips->Reset();
     }
+
+  // discard Links and Cells
+  this->DeleteLinks();
+  this->DeleteCells();
 }
 
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