Intersection with empty input should return dimension-appropriate empty geometry

[peterstace]

Currently, Intersection returns GEOMETRYCOLLECTION EMPTY when one or both inputs are empty:

if a.IsEmpty() || b.IsEmpty() {
    return Geometry{}, nil
}

However, when envelopes are disjoint (but inputs are non-empty), it returns a dimension-appropriate empty geometry:

if envelopesDisjoint(a, b) {
    return createEmptyResult(minInt(a.Dimension(), b.Dimension())), nil
}

For consistency, the empty input case should also return createEmptyResult(minInt(a.Dimension(), b.Dimension())). This would allow combining the two conditions:

if a.IsEmpty() || b.IsEmpty() || envelopesDisjoint(a, b) {
    return createEmptyResult(minInt(a.Dimension(), b.Dimension())), nil
}

The existing tests expect GEOMETRYCOLLECTION EMPTY for empty inputs, so they would need to be updated.