safely handle cases where there are no scene layers

app/components/download/create-mesh.tsx

@@ -56,7 +56,8 @@ export default async function createMesh(scene: WebScene, extent: Extent, signal
   const ground = scene.ground;
 
   const layers = scene.allLayers.filter(layer => layer.type === "scene").toArray() as SceneLayer[];
-  const sr = layers.at(0)!.spatialReference;
+
+  const sr = layers.at(0)?.spatialReference ?? extent.spatialReference;
 
   const features = (await Promise.all(layers.map(layer => extractFeatures(layer, extent, signal)))).flat();
   const projectedExtent = projection.project(extent, sr) as Extent;

app/routes/$scene/route.tsx

@@ -3,14 +3,12 @@ import { Suspense, lazy } from "react";
 import { redirect, useLoaderData, useRouteError } from "@remix-run/react";
 import Sidebar from "~/components/sidebar/sidebar";
 import invariant from "tiny-invariant";
-import SCENES from "~/data/scenes";
 import { ViewUI } from "../../components/arcgis/views/scene-view/scene-view-ui";
 import { CalciteAction, CalciteNavigation, CalciteNavigationLogo, CalciteNavigationUser, CalciteScrim } from "@esri/calcite-components-react";
 import { SelectionAction } from "../../components/selection/selection-button";
 import GraphicsLayer from "~/components/arcgis/graphics-layer";
 import SelectionExtent from "../../components/selection/selection-graphic";
 import WalkthroughPopover from "~/components/walk-through/walk-through-popover";
-import { load as loadProjectionEngine } from "@arcgis/core/geometry/projection";
 import SelectionErrorAlert from "~/components/selection/selection-error-alert";
 import { useSceneListModal } from "~/components/scene-list-modal/scene-list-modal-context";
 import { useAccessorValue } from "~/hooks/reactive";