BUG: image/pad: now copy input data type (fixes issue 1362)
BUG: image/pad: now copy input data type (fixes issue 1362)

Former-commit-id: 2b06e7a14fd10013d16df9d4b8d9c5d5ffc66879
neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox