Release Vantage viewer after failed loads [skip ci]

launcher/src/components/VantageMap.svelte

@@ -124,8 +124,18 @@
       const body = result.data ? Uint8Array.from(atob(result.data), (c) => c.charCodeAt(0)) : null;
       return new Response(body, { status: result.status, headers: result.etag ? { etag: result.etag } : {} });
     } }) : Promise.resolve(world);
-    return vantage.VantageViewer.mount(host, { world: await source, view: 'top', players: { offline: false } });
+    const resolved = await source;
+    if (cancelled) return null;
+    const v = new vantage.VantageViewer(host, { view: 'top', players: { offline: false } });
+    try {
+      await v.load({ world: resolved, view: 'top' });
+      return v;
+    } catch (e) {
+      v.dispose();
+      throw e;
+    }
     }).then((v) => {
+      if (!v) return;
       if (cancelled) { v.dispose(); return; }
       viewer = v;
       ready = true;