InfoGain: Remove zero columns.
InfoGain: Remove zero columns.

When the data domain is not fully represented (i.e. no appearances of some value of Discrete attribute), there are zero columns in contingency array. These columns are now removed to be able to devide by np.sum(D, axis=0) when calculating entropy.

qPCR4vir/orange3,cheral/orange3,qPCR4vir/orange3,cheral/orange3,marinkaz/orange3,marinkaz/orange3,cheral/orange3,kwikadi/orange3,marinkaz/orange3,marinkaz/orange3,cheral/orange3,qPCR4vir/orange3,marinkaz/orange3,kwikadi/orange3,kwikadi/orange3,qPCR4vir/orange3,kwikadi/orange3,kwikadi/orange3,marinkaz/orange3,kwikadi/orange3,qPCR4vir/orange3,qPCR4vir/orange3,cheral/orange3,cheral/orange3