Improve error message when soil or geology input data is not masked properly
When soil_class.asc or geology_class.asc are not masked properly and contain NoData-Values where other morphological input data sets are defined, following error will be thrown:
***ERROR: Class -9999 is missing
in input file soil_classdefinition.txt ...
Since -9999 is a NoData value here and not a valid class ID, the user should get the advice to check his masking routine.