Only do geometries.geoms when the attribute is present.

[EmileSonneveld]

#519
@copilot review

[chatgpt-codex-connector]

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[soxofaan]

features_ids_from_index is already a bit obscure because of lack of type annotations. Adding this if here makes it worse I think

I would fully eliminate features_ids_from_index and just do the list comprehension inline in the if-else below. Something like

        if isinstance(self._regions, GeometryCollection):
            ...
            feature_ids = ["feature_%d" % i for i in range(len(self._regions))]
        elif isinstance(self._regions, DriverVectorCube):
            ...
            feature_ids = (list(feature_ids) if feature_ids is not None
                           else ["feature_%d" % i for i in range(self._regions.geometry_count())])
        else:
            raise ValueError(self._regions)

(Note: GeometryCollection is something we should get rid of, so this would prepare more cleanly for that)