The owner retrieving items for a pubsub node should not require a subscription id when there is only 1 subscription

Attempting to retrieve items for a node will fail when there was no subscription id specifed in the request, even though the user only has 1 subscription. This should work if there are not multiple subscriptions.

This occurs for the owner only after creating the node, since they are automatically subscribed when the node is created. This appears to be a defect, since there is nothing in the spec to support this behaviour.