Fixing the unfolding (issue #98)

Fixing the issue #98. Does this look about right?
Ignore white space in the [diff](https://github.com/BristolTopGroup/NTupleProduction/pull/101/files?w=1) for clarity.
It should have 0 contribution to the unfolding as we are not using the gen-fakes and all reco variables are guaranteed to have a lepton due to the offline selection.