handling NaN in runoff input data

[nmizukami]

If compiled with a flag -ffpe-trap=invalid and your runoff includes NaN as Fillvalue in the netCDF, the code stops with the compiler's message : Program received signal SIGFPE: Floating-point exception - erroneous arithmetic operation or similar to this.

The error happen at

where ( abs(dummy - forc_data_in%fillvalue) < verySmall ) dummy = realMissing

in read_runoff.f90.

Here fillvalue is NaN and the fortran trap dummy - forc_data_in%fillvalue as an invalid answer.

The code may need to handle NaN fillvalue by changing NaN to realMissing.