BUG: RSS label image type bug fixed

previously char pixel type is used for input/output label images.
but that is not enough for larger label values. this causes crash.
I changed it to short type to hold more label values.
Tested on previous fail cases and works now. Linux 64

From: Yi Gao <yi.gao@gatech.edu>

git-svn-id: http://svn.slicer.org/Slicer4/trunk@22086 3bd1e089-480b-0410-8dfb-8563597acbee