Update app.py

app.py

@@ -105,7 +105,7 @@ async def get_track_download_url(track_id: str) -> str:
 async def track_dl():
     track_id = request.json.get('track_id')
     dl_url = await get_track_download_url(track_id)
-    if dl_url:
+    if is_valid_url(dl_url):
         result = {"url": dl_url}
         return jsonify(result)
     else: