return zero for equivalent points

This avoids a ping-pong effect in the PSSP case.

It fixes the validity check of the following input br50noseg.cin:

s -50 -20    0 +30
s   0 +30  +50 -20
p -20   0
p +20   0

Signed-off-by: Panagiotis Cheilaris <philaris@cs.ntua.gr>

Segment_Delaunay_graph_Linf_2/include/CGAL/Segment_Delaunay_graph_Linf_2/Voronoi_vertex_sqrt_field_new_C2.h

@@ -1968,6 +1968,15 @@ private:
             return POSITIVE;
           }
 
+          if ((v_type == PSS) and (not is_q_hv) and (not is_r_hv)) {
+            if (test == EQUAL) {
+              CGAL_SDG_DEBUG(std::cout
+                  << "debug equivalent points and two non-hv segments,"
+                  << " thus return zero" << std::endl;);
+              return ZERO;
+            }
+          }
+
         }
       } else {
         // tocheck and tofix