Interpolation of external datasets leads to crash when no valid data in a subdomain

[docguibou]

This problem generally appears at high resolution (=<12km) when using large domains and 20+ cores for neXtSIM.
There is then a chance that the data used to initialize the sea ice (e.g. sea ice thickness from PIOMAS, TOPAZ or CS2SMOS) do not cover completely the full domain. If it happens that the model domain division for parallel computing leads to one subdomain with no valid data in the init. dataset, the model crashes as the default value of the data given in this is case is 10,000. Often, this crash comes without an error message.

A temporary fix, too dodgy to be merged with the main code, is to edit this value in externaldata.cpp and set it to 0.
Other possibilities to fix it would be to use an external routine to create an artificial restart file, or add another setup.ice-type that would read a file called for instance init_ice_nextsim.nc in which data are given on a grid (after off-line interpolation) that would work for the domain we want to use.