Handling empty feature table

[TimothyStephens]

Hi,

Thank you for your work on whokaryote.

I have encountered a bug when whokaryote is run on very small MAGs without any valid features identified. A bit of an edge case I know. The error arrises from predict_class.py: line 90 The features DataFrame is empty, which causes a ValueError to be returned by predictions = loaded_rf.predict(features). ValueError: Found array with 0 sample(s) (shape=(0, 9)) while a minimum of 1 is required.

A work around for this problem is to replace line 90 with the following.

    predictions = []
    if not features.empty:
        predictions = loaded_rf.predict(features)

I believe that it should preserve the normal behavior of whokaryote.

Thanks, Tim.