OPT: concat_transfo: now check if warping field not created (and output error)
OPT: concat_transfo: now check if warping field not created (and output error)

Former-commit-id: 97558606c0df102a98ae7705875241d7b86ed4a7
Former-commit-id: a6e81386e8402bd46fb15d8c98b6e5b539996a47
3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox