Potential overflow when calculating exp

[HaisongDing]

eesen/asr_egs/wsj/utils/nnet_notf.py

Line 228 in c64c152

scoreMatExp = np.exp(np.asarray(mat))

One simple fix would be:
mat_array = np.asarray(mat)
mat_array = (mat_array.transpose() - mat_array.max(axis=1)).transpose()
scoreMatExp = np.exp(mat_array)