scene: fix wlr_scene_render_output offset

When providing non-zero layout-local coordinates to
wlr_scene_render_output, the viewport should be translated by the
given values. However the viewport was translated by the opposite
values: when giving 42,42 the viewport's position would be set to
-42,-42.

types/wlr_scene.c

@@ -426,7 +426,7 @@ void wlr_scene_render_output(struct wlr_scene *scene, struct wlr_output *output,
 			.output = output,
 			.damage = damage,
 		};
-		scene_node_for_each_node(&scene->node, lx, ly,
+		scene_node_for_each_node(&scene->node, -lx, -ly,
 			render_node_iterator, &data);
 		wlr_renderer_scissor(renderer, NULL);
 	}