Add fix nan

[davide-f]

Change proposed in this Pull Request

Simple fix of nan values in hydro function.
In the hydro function a normalization of the matrix indicator is performed; yet some nan values may be created.
To avoid the formation of nan values, in this PR they are forced to zero.

This is a feature needed for earth analysis and originally implemented intp #245.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• I tested my contribution locally and it seems to work fine.
• I locally ran pytest inside the repository and no unexpected problems came up.
• I have adjusted the docstrings in the code appropriately.
• I have documented the effects of my code changes in the documentation doc/.
• I have added newly introduced dependencies to environment.yaml file.
• I have added a note to release notes doc/release_notes.rst.
• I have used pre-commit run --all to lint/format/check my contribution

[euronion]

Do you know what causes the nan and inf values to appear?

[davide-f]

When using this in the past, I had some nans reported but I don't recall exactly the reason, I have no experience of inf, but that function also hands them.
Some times since that normalization is performed, the sum of the row was zero.

[davide-f]

It could be when the hydrobasins shapes and cutout regions do not exactly match and/or when the hydrobasin is not complete.
This is the case for Large regions where the source of a river starts very far from a country.