BUG: adjust resample interpolation type for label maps

The volumes logic method ResampleVolumeToReferenceVolume can be
called with an input label map scalar volume, check for that case.
For label maps we don't want to do a linear interpolation over any data
present as that could result in values not defined in the color look
up table, so use the nearest neighbour filter option instead.

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23781 3bd1e089-480b-0410-8dfb-8563597acbee