The reported Freestyle warnings were due to wrong normals of filled faces at both ends
of a 2D extruded curve. The problem is detailed in the comment #19 of T39669.
The cause of the bug was an inconsistency in the use of vertex indices between
BKE_mesh_nurbs_displist_to_mdata() and init_render_curve() in the case of
DispList::type equal to DL_INDEX3.
This commit also fixes a related bug that the normals of filled faces were not inverted
when a scale of the curve object is set to a negative value (e.g., the Z scale was -1).
Reviewers: campbellbarton
Reviewed By: campbellbarton
Differential Revision: https://developer.blender.org/D532
f8554ed61a