OverlayNG should return Point for intersection with zero-length LineString

[pramsey]

To match with the RelateNG logic, overlay should return a Point for intersection between Polygon and zero-length LineString. Currently it returns an empty LineString.

[dr-jts]

This behaviour needs to apply in multiple situations. E.g.

• Area with zero-length LineString
• Area with MultiLineString containing zero-length element
• Linear geometry with (Multi)LineString with zero-length element
• Point geometry with (Multi)LineString with zero-length element

In general, the intersection of a zero-length LineString element with any geometry should produce an equivalent Point output (unless it is covered by another linear input element).

The semantics for other overlay operations need to be decided and implented as well.