PyNEMO crashes with mask==False but runs with mask==True
Created by: thopri
If bathymetry has a line of zeros in its outer edges then this currently causes PyNEMO to crash if mask==false is selected. PyNEMO in this instance will try and make its own mask using the bathymetry file. However zeros at the outer edge will make it think there is land along all boundaries resulting in it not being able to create the mask. However if a valid mask file is provided it will work as PyNEMO doesn't use the bathymetry in mask creation.
Initial fix will to be to add an try except so that this issue is caught and user is informed about problem rather having an opaque error. It is anticipated that functionality will be added so that PyNEMO can handle zeros in the outer edges of the bathymetry but for short term PyNEMO either needs a valid mask file or bathymetry values right up to the boundaries.