fimex creates files with corrupt data without error code

[heikoklein]

Hi,
the newest fimex version create netcdf-files with corrupt data without error-code:

e.g.
fimex --extract.selectVariables WDEP_SOX 'https://thredds.met.no/thredds/dodsC/data/EMEP/2019_trends_EEA/EMEP01_L20EC_rv4_33_day.met2016_emis2017.nc' out.nc4
WARN: formula term 'ps' specifies unknown variable 'PS' in /build/fimex-1.5-1.5.0/src/coordSys/CF1_xCoordSysBuilder.cc at line 472
WARN: formula term 'ps' specifies unknown variable 'PS' in /build/fimex-1.5-1.5.0/src/coordSys/CF1_xCoordSysBuilder.cc at line 472
curl error details:
ERROR: exception while reading variable 'WDEP_SOX' at unlimited dim position 75; using _FillValue; message: CDMException: NetCDF: I/O failure in /build/fimex-1.5-1.5.0/src/NetCDF_CDMWriter.cc at line 718

In this case, a network error lead to an undelivered data request. fimex just writes the output and exits with code 0.

In an operational context, error output is not read unless the program fails, e.g. has a non-zero exit code.

This problem was introduced in 2ce00fb.

Fimex should give a non-zero exit code when errors occur. Fimex should not continue operations (unless explicitly requested) after an error occured.