Fix of [2.3.0-alpha4] Crash - several models cause crash when slicing #5208

Fixed some issues in internal anchors of the Adaptive Cubic infill.
The ugly and dangerous implicit casting operators in Line, MultiPoint,
Polyline and Polygon were made explicit.

src/libslic3r/ModelArrange.cpp

@@ -49,7 +49,7 @@ Slic3r::arrangement::ArrangePolygon get_arrange_poly(const Model &model)
             std::copy(pts.begin(), pts.end(), std::back_inserter(apts));
         }
     
-    apts = Geometry::convex_hull(apts);
+    apts = std::move(Geometry::convex_hull(apts).points);
     return ap;
 }