callback fixes

app/app.py

@@ -1050,8 +1050,9 @@ class DeviceCallback(Resource):
       await db.execute(query='REPLACE INTO callback_urls (device, url) VALUES (:device, :url)',
                        values={'device': device,'url': url})
     else:
-      url = await db.fetch_one(query='SELECT url FROM callback_urls WHERE device = :device',
+      row = await db.fetch_one(query='SELECT url FROM callback_urls WHERE device = :device',
                                values={'device': device})
+      url = row['url']
     return successCallbackURL(device, url)
 
 manager.connect()