sq_circumradius cannot be computed on an infinite facet

there was no need to check if a face is in domain, but we still need to check
whether it is infinite

Mesh_2/include/CGAL/Mesh_2/Mesh_global_optimizer_2.h

@@ -307,7 +307,8 @@ private:
     // Find the minimum value
     do
     {
-      min_sqr = (std::min)(min_sqr, sq_circumradius(face));
+      if (!cdt_.is_infinite(face))
+        min_sqr = (std::min)(min_sqr, sq_circumradius(face));
       face++;
     }
     while(face != end);