As the test shows, we can create geometries that have less than two vertices
after eliminating duplicates. Calling d2d_cdt_triangulate() on those would
lead to infinite recursion. In principle we could now get rid of the original
vertex count check, but it seems cheap enough that it's worth keeping in order
to avoid some unnecessary work in the somewhat more common case that we have
less than three vertices before duplicate removal.

Based on a patch by Changsheng Chen.
Signed-off-by: Henri Verbeet <hverbeet@codeweavers.com>
Signed-off-by: Alexandre Julliard <julliard@winehq.org>