metal: clear damage before adding full damage

src/backends/metal/video.rs

@@ -3332,6 +3332,7 @@ impl RenderBuffer {
     pub fn damage_full(&self) {
         let dmabuf = self.dev_bo.dmabuf();
         let rect = Rect::new_sized_unchecked(0, 0, dmabuf.width, dmabuf.height);
+        self.damage_queue.clear_all();
         self.damage_queue.damage(&[rect]);
     }
 }