unbound local error in rivers method

[DirkEilander]

The else statement in rivers should be lowered to fix a potential unbound local error if no river geoms is found and not river mask is found.

hydromt_wflow/hydromt_wflow/wflow.py

Line 2107 in 4f26392

return gdf

This error is raised when building the docs for the update_model_gauges.ipynb example (see action referenced below), but was not raised before. We should carefully check why both the rivers geom and river mask map are not available anymore!

https://github.com/Deltares/hydromt_wflow/actions/runs/3187682388/jobs/5260892285

[hboisgon]

This seems to be linked to #108 , the model with updated gauges is not created so no rivers can be found. But anyway indeed the unbound local error should be removed in self.rivers