possible typo in the Backprojector of FBP_opencl in nabu.reconstruction

Hi Pierre,

There is a possible typo in the Backprojector of FBP_opencl in nabu.reconstruction, line 35 I suppose that you mean None with capital N rather than none with lower case n, right?

if scale_factor is not none:

Otherwise we get NameError: name 'none' is not defined

Thank you in advance.