logic in ProjMatrixByBinUsingRayTracing set_ functions wrong for already_set_up

[KrisThielemans]

I introduced lines like this

STIR/src/recon_buildblock/ProjMatrixByBinUsingRayTracing.cxx

Line 140 in 0307f8d

this->already_setup = (this->restrict_to_cylindrical_FOV == val);

but this can mean that calling a set function with the current value sets already_set_up=true, even if it wasn't set-up yet.