COMP: add GetPointer to vtkNew'd matrices
On ubuntu 16.04 (gcc 5.4) the vtkMatrix4x4 is not coerced to a pointer automatically. Adding GetPointer is consistent with other usages in this file and solves the compile issue.
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On ubuntu 16.04 (gcc 5.4) the vtkMatrix4x4 is not coerced to a pointer automatically. Adding GetPointer is consistent with other usages in this file and solves the compile issue.