BUG: fixed add_suffix@sct_utils to account for nii.gz extensions
BUG: fixed add_suffix@sct_utils to account for nii.gz extensions

Former-commit-id: 56a2e1839b15c882b74606ad9479f221f9803f76 [formerly 2ac7c3c6ea904cf0cce23a7cc49b603d310a6c98]
Former-commit-id: c6b1335bac39c8633636b83caed6ba13cd1e4341
Former-commit-id: 18f5f45eb2e70e2ccebb3750dfab66cfb886b51d
neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox