fix(faroro_pet_feeder): Last feed amount is optional

On a newly unboxed device, there is no last feed.

Issue #3528

custom_components/tuya_local/devices/faroro_pet_feeder.yaml

@@ -45,6 +45,7 @@ entities:
       - id: 15
         name: sensor
         type: integer
+        optional: true
   - entity: sensor
     name: Voice times
     icon: "mdi:account-voice"