fix memory leak in vtkSTLReader when vtkSTLReader failed to read STL file
When some error in the STL file, the vtkSTLReader failed to read it, the vtkSTLReader have some memory by not release some pointer it allocated before.
When some error in the STL file, the vtkSTLReader failed to read it, the vtkSTLReader have some memory by not release some pointer it allocated before.