Load presets into the new C++ class.

lib/Slic3r.pm

@@ -163,6 +163,7 @@ sub thread_cleanup {
     *Slic3r::Surface::Collection::DESTROY   = sub {};
     *Slic3r::Print::SupportMaterial2::DESTROY = sub {};
     *Slic3r::TriangleMesh::DESTROY          = sub {};
+    *Slic3r::GUI::PresetBundle::DESTROY     = sub {};
     return undef;  # this prevents a "Scalars leaked" warning
 }