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

3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox