The commit rBb718d659c9a5 fixed the BLI_scanfill_calc_ex that flipped
the normal of the tessellated polygons.
But this commit ignored that the drawing code and mesh conversion code
makes a kind of normal readjustment for DL_INDEX3 type displists.
I don't know why this readjustment exists but it seems to be a kind of workaround.
This patch proposes to create a consistency in scanfill, drawing and mesh
conversion with respect to the normal of such displist (DL_INDEX3).