data/ml/answer-train.py: Fix crashes when testing on a tiny sample
data/ml/answer-train.py: Fix crashes when testing on a tiny sample

vineetk1/yodaqa,vineetk1/yodaqa,vineetk1/yodaqa,Martinfx/yodaqa,vineetk1/yodaqa,Martinfx/yodaqa,Martinfx/yodaqa,Martinfx/yodaqa,Martinfx/yodaqa,Martinfx/yodaqa,vineetk1/yodaqa,vineetk1/yodaqa