Fixed wrong Miter limit when offsetting contours to build a Z-graph

of layer islands.
Partial fix of SPE-1729 #10632

src/libslic3r/Layer.cpp

@@ -81,7 +81,8 @@ void Layer::make_slices()
     // Top / bottom surfaces must overlap more than 2um to be chained into a Z graph.
     // Also a larger offset will likely be more robust on non-manifold input polygons.
     static constexpr const float delta = scaled<float>(0.001);
-    co.MiterLimit = scaled<double>(3.);
+    // Don't scale the miter limit, it is a factor, not an absolute length!
+    co.MiterLimit = 3.;
 // Use the default zero edge merging distance. For this kind of safety offset the accuracy of normal direction is not important.
 //    co.ShortestEdgeLength = delta * ClipperOffsetShortestEdgeFactor;
 //    static constexpr const double accept_area_threshold_ccw = sqr(scaled<double>(0.1 * delta));