Invalid LinearRing is reported as valid

[dr-jts]

Certain kinds of LinearRings with self-intersections are reported as valid by Geometry.isValid(). For example:

LINEARRING (40 90, 90 90, 10 10, 90 10, 40 90)

This is caused by a bug in the way IsValidOp analyzes the self-intersections. Roughly, if the self-intersection is to the left of the ring endpoint, it is not detected as being invalid.

Originally reported as Shapely-1133