Evap: Slight inconsistency between possible sunshine duration and extraterrestrial radiation

[tyralla]

See the fourth line in the "hourly simulation" integration test. Possibly not a big deal, but we should investigate the reason later.

There is already (a related?) critical discussion in the documentation on method Calc_ExtraterrestrialRadiation_V1.

My first guess is, that using the max function is too simple and causes inconsistency with the possibly sunshine duration:

            flu.extraterrestrialradiation = max(
                12.0
                * 4.92
                / d_pi
                * flu.earthsundistance
                * (
                    (
                        (d_omega2 - d_omega1)
                        * modelutils.sin(der.latituderad)
                        * modelutils.sin(flu.solardeclination)
                    )
                    + (
                        modelutils.cos(der.latituderad)
                        * modelutils.cos(flu.solardeclination)
                        * (modelutils.sin(d_omega2) - modelutils.sin(d_omega1))
                    )
                ),
                0.0,
            )