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.
I'm not sure. Other variables (like MT/WPT) are set to -1 in the non-semileptonic case, so I think we could keep it the same for consistency. However, HT and MET can have genuine values in the fakes case. What effect do you think it would have on the unfolding?