plot3d(facets): Extra blinking facets are plotted (+ edges linked to (0,0,0))

Reported by Samuel GOUGEON (@sgougeon)

Originally assigned to Caio SOUZA

-- Bug description --


plot3d(facets): Extra blinking facets are plotted (+ edges linked to (0,0,0)). Was OK with 4.1.2


-- Scilab error message --


Wrong display. 
Drag and drop the attached scg file (refused by 4.1.2)
See the code below.


-- How to reproduce the bug --


Created an attachment (id=2067)
plot3d(facets): Parasitic edges and facets are drawn

X = [0 10 10 7  6.5 3.5  3 0 0]';
Y = [0 0 10 10  2 2  10 10 0]'; 
Z = zeros(X);
clf, plot3d(X($:-1:1),Y($:-1:1),zeros(X))
ca=gca(); ca.rotation_angles=[76 236];