SBM variables vwc_root and vwc_percroot can have NaN values

[verseve]

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Reproducible Example

A wflow_sbm model with zero rootingdepth values.

Current behaviour

When the rootingdepth is zero, vwc_root and vwc_percroot result in NaN.

Desired behaviour

When the rootingdepth is zero, vwc_root and vwc_percroot should be set at zero.

Additional Context

No response

[verseve]

Actually, after a bit more thinking these NaN values are fine. The Wflow ZMQ server (JSON) cannot deal with NaNs, see issue #392, and this should be fixed there.