feat(hatch): add multi-region selection

Refs #532

src/scene/mod.rs

@@ -3181,6 +3181,7 @@ impl Scene {
             world_origin: [0.0, 0.0],
             boundary: Arc::new(vec![[x0, y0], [x1, y0], [x1, y1], [x0, y1], [x0, y0]]),
             boundary_wcs: None,
+            boundary_exterior: None,
             pattern: crate::scene::model::hatch_model::HatchPattern::Solid,
             name: "SOLID".to_string(),
             color: self.paper_bg_color,