BUG: Fix Nifti IO read with large images.

Prevent overflow of int with large images.

Suggested-by: Kris Thielemans <kris.f.thielemans@gmail.com>

Change-Id: I020a53d97db359b7ae4d9d4c61f98e382a2dcaa1
Merge topic 'LargeNifti_release'

1aa73298 BUG: Fix Nifti IO read with large images.