Fix Eigen error

Fixes http://www.pcl-users.org/simple-renderView-example-td4035597.html

```
test_pcl: /usr/include/eigen3/Eigen/src/LU/Inverse.h:294: void Eigen::internal::inverse_impl<MatrixType>::evalTo(Dest&) const [with Dest = Eigen::Matrix<float, 4, 4>; MatrixType = Eigen::Matrix<float, 4, 4>]: Assertion `( (Size<=1) || (Size>4) || (extract_data(m_matrix)!=extract_data(dst))) && "Aliasing problem detected in inverse(), you need to do inverse().eval() here."' failed.
```