Fixes gaps created around the 3D honeycomb infill. The bug has been

introduced during the C++ porting of the original Perl code.

xs/src/libslic3r/Fill/Fill3DHoneycomb.cpp

@@ -148,7 +148,6 @@ void Fill3DHoneycomb::_fill_surface_single(
 {
     // no rotation is supported for this infill pattern
     BoundingBox bb = expolygon.contour.bounding_box();
-    Point       size = bb.size();
     coord_t     distance = coord_t(scale_(this->spacing) / params.density);
 
     // align bounding box to a multiple of our honeycomb grid module
@@ -160,8 +159,8 @@ void Fill3DHoneycomb::_fill_surface_single(
     Polylines   polylines = makeGrid(
         scale_(this->z),
         distance,
-        ceil(size.x / distance) + 1,
-        ceil(size.y / distance) + 1,
+        ceil(bb.size().x / distance) + 1,
+        ceil(bb.size().y / distance) + 1,
         ((this->layer_id/thickness_layers) % 2) + 1);
     
     // move pattern in place