Wrong monolane for an intersection between an arc and another arc

[basicNew]

Test to reproduce:

    def broken_intersection_on_two_lanes_city(self):
        """
                      (10,50)
                         |
                        |    __--- (50,20)
        (-50,0) ------- + ---
                        |
                        |
                      (0,-50)
        """
        city = City("Broken intersection - Two lanes")

        s1 = Street.from_control_points([Point(-50, 0), Point(0, 0), Point(50, 20)])
        s1.name = "s1"

        s2 = Street.from_control_points([Point(0, -50), Point(0, 0), Point(10, 50)])
        s2.name = "s2"

        city.add_intersection_at(Point(0, 0))

        city.add_road(s1)
        city.add_road(s2)

        return city