Fix Camera2D crash when edited scene root is null

scene/2d/camera_2d.cpp

@@ -41,7 +41,7 @@ void Camera2D::_update_scroll() {
 	if (Engine::get_singleton()->is_editor_hint()) {
 		queue_redraw();
 		// Only set viewport transform when not bound to the main viewport.
-		if (get_viewport() == get_tree()->get_edited_scene_root()->get_viewport()) {
+		if (get_tree()->get_edited_scene_root() && get_viewport() == get_tree()->get_edited_scene_root()->get_viewport()) {
 			return;
 		}
 	}