OPT: remove blank line after each invocation of sct_extract_metric when using -overwrite 0
OPT: remove blank line after each invocation of sct_extract_metric when using -overwrite 0

Former-commit-id: 96bba91e7cfb9a0e10594aef20a37e8dc01e36c2 [formerly d605c7b821696df2e4675318873fedcd1ada033f]
Former-commit-id: 1d02e0c241017b86f007fe5621b144fb16e4f73d
Former-commit-id: b40b511edec67923e53a4a98af4c063fe3623cd1
neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox