exit properly (?)

src/main.rs

@@ -109,6 +109,7 @@ fn main() {
 						(show_crown_gear, show_crown_cutter) = (show_crown_cutter, show_crown_gear);
 						(show_rack_gear, show_rack_cutter) = (show_rack_cutter, show_rack_gear);
 					}
+					DrawEvent::Closed => break 'main,
 					_ => {}
 				}
 			}