UnboundLocalError in evaluation.py

[omidrohanian]

In the evaluation file, f1_positivesand f1_negatives are defined within conditionals. I think it is better if they are initialized beforehand as this might cause UnboundLocalError on line 31. Those conditions cannot both hold true all the time (e.g. a system that produces zero true positives but a lot of true negatives).

[dpaperno]

Thank you Omid, we have fixed this following your suggestion!