Quad.copy discards point3

[Norbert515]

  /// Create a quad as a copy of [other].
  Quad.copy(Quad other)
      : _point0 = new Vector3.copy(other._point0),
        _point1 = new Vector3.copy(other._point1),
        _point2 = new Vector3.copy(other._point2),
        _point3 = new Vector3.copy(other._point2);

It should be:

       _point3 = new Vector3.copy(other._point3);