Fix png inputs sCal flag

Due to change of behavior with libpng, where files have been updated
with a METER sCal field.

Change-Id: Ic7d8bcbda32143c31e31d0a5213f1434728df008
Merge topic 'SIMPLEITK_589_FixPNGsCalField' into next

8d87af8b Fix png inputs sCal flag