Large cubic causes crash during flattening

[LaurenzV]

Test:

 #[test]
    fn large_cubic() {
        let mut path = BezPath::new();
        path.move_to((-2.1351245891339424e19, -3.976870325297853e18));
        path.curve_to((-2.1351245891339424e19, -3.976870325297879e18), (-2.1350093033635213e19, -3.9766555947095035e1), (-2.1348670911586615e19, -3.9763907111049165e1));
        path.close_path();
        fill(
            Level::try_detect().unwrap_or(Level::fallback()),
            path,
            Affine::IDENTITY,
            &mut vec![],
            &mut FlattenCtx::default()
        );
    }