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)

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