Fix variableOffsetPP for the case when global attributes instrument_nominal_depth and / or time_deployment_start exist but set to empty.
Fix variableOffsetPP for the case when global attributes instrument_nominal_depth and / or time_deployment_start exist but set to empty.

ggalibert/imos-toolbox,ggalibert/imos-toolbox,ggalibert/imos-toolbox,ggalibert/imos-toolbox,ggalibert/imos-toolbox