BUG: Fix Lua test template for no_return_image

The writing of the resulting image was outside the no_return_image
template conditional block.

Change-Id: I06c25b6361a59ad51a6d92cd19384779dfdd51dc
Merge topic 'SIMPLEITK-490_Uset1functionForLabelStatisticsImageFilter' into next

fe4c4009 BUG: Fix Lua test template for no_return_image