BUG: use size_t for conversion to numpy array

std::accumulate was implicitly using unsigned int as a template
parameter. The integer is not explicitly a size_t to ensure the type
is large enough.

Change-Id: I2b078f39cea0882126b7739c18557e85fde74307
STYLE: fix indentation style

Change-Id: Id079e342331fa5e1ed4333041707e9bbe0f080df
Merge topic 'SIMPLEITK-424_Fix4GBGetImageFromArray'

224870d STYLE: fix indentation style
1170184 BUG: use size_t for conversion to numpy array