BUG: process_segmentation: changed parser type to ‘str’ so that it does not fail if optional file does not exist
BUG: process_segmentation: changed parser type to ‘str’ so that it does not fail if optional file does not exist

Former-commit-id: 38b05c4d62802ebc6382ad0b7293185330f6d240
neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox