FIX: idwtn should treat None coefficients as described in the docstring.
FIX: idwtn should treat None coefficients as described in the docstring.

This change also makes is consistent with the existing idwt2 behavior

PyWavelets/pywt,rgommers/pywt,PyWavelets/pywt,rgommers/pywt,grlee77/pywt,rgommers/pywt,grlee77/pywt,rgommers/pywt