lf94

I've built CuraEngine master branch from source but I can't seem to use it with Cura 4.11 AppImage. I've tried using `Cura --external-backend `, and `CuraEngine connect ...`, but when hitting "Slice", CuraEngine's connection is closed immediately. I have made no changes to CuraEngine. I've opened an issue on GitHub as well: https://github.com/Ultimaker/CuraEngine/issues/1510