[Enhancement] Directional Variogram: control division by zero warnings

[SimonMolinsky]

Is your feature request related to a problem? Please describe.

Describe the solution you'd like Check why this warning occurs, and then write a condition to control the part of a calculation where it is present. Use DEM data for tests.

Describe alternatives you've considered Do nothing and suppress warnings, but it could be dangerous and leads to computational errors.

Additional context n/a