add except for varkey_list loop in dfmt.preprocess_merge_meteofiles_era5()

[veenstrajelmer]

the varkey_list loop currently does not have an else/except, so if one would supply varlist_list = [['msl','u10n','v10n','chnk','d2m','t2m','ssr','strd','mer','mtpr']], it will silently do nothing

dfm_tools/dfm_tools/modelbuilder.py

Line 167 in 03cabed

if varkey_list == ['msl','u10n','v10n','chnk']:

Also when passing separate quantities it will fail in this case. At least add an exception.

Better approach would be to create a dictionary of abbreviations/quantities and remove the if-loop: #887