BUG: N4ITKBiasFieldCorrection - Change output type to float

Cast of the output to the input type led to occasional overflows. Output of this
module is inherently floating point, as it is a multuplication of the recovered
bias field by the input image.

From: Andrey Fedorov <fedorov@bwh.harvard.edu>

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23330 3bd1e089-480b-0410-8dfb-8563597acbee