COMP: Fix bug in writing origins to MGH files

Waiting Slicer makes use of the ITK remote module "itkMGHImageIO" (issue #3410),
this commit has been back-ported from Slicer/itkMGHImageIO@13f5e11ef.

It also has been tested by Hans as part of ITK.

Test project /Users/johnsonhj/Dashboard/src/ITK-ccache
Start 2065: MGHIOInDoxygenGroup
1/7 Test #2065: MGHIOInDoxygenGroup .............. Passed 0.09 sec
Start 2066: MGHFactoryCreationTest
2/7 Test #2066: MGHFactoryCreationTest ........... Passed 0.15 sec
Start 2067: MGHReadImagesTest_mgz
3/7 Test #2067: MGHReadImagesTest_mgz ............ Passed 3.77 sec
Start 2068: MGHReadImagesTest_mgh
4/7 Test #2068: MGHReadImagesTest_mgh ............ Passed 0.49 sec
Start 2069: MGHReadImagesTest_mgh.gz
5/7 Test #2069: MGHReadImagesTest_mgh.gz ......... Passed 3.88 sec
Start 2070: itkMGHIOInternalTests
6/7 Test #2070: itkMGHIOInternalTests ............ Passed 0.07 sec
Start 2071: itkMGHIOOriginTest
7/7 Test #2071: itkMGHIOOriginTest ............... Passed 3.58 sec

More details here: http://review.source.kitware.com/#/c/12771/

From: Kent Williams <norman-k-williams@uiowa.edu>

git-svn-id: http://svn.slicer.org/Slicer4/trunk@22485 3bd1e089-480b-0410-8dfb-8563597acbee