If no App Store subscriptions option are available return empty optio…

…ns object (#3188)

Task/Issue URL:
https://app.asana.com/0/1203936086921904/1207934463147478/f

**Description**:
In case no App Store subscription objects are available we should return a proper SubscriptionOptions.empty object.

DuckDuckGo/Subscription/UserScripts/SubscriptionPagesUseSubscriptionFeature.swift

@@ -205,7 +205,7 @@ final class SubscriptionPagesUseSubscriptionFeature: Subfeature, ObservableObjec
         } else {
             os_log("Failed to obtain subscription options", log: .subscription, type: .error)
             setTransactionError(.failedToGetSubscriptionOptions)
-            return nil
+            return SubscriptionOptions.empty
         }
     }