Fixes Document Workspace Info Link error

Ensures that `_unique` has value. This was previously throwing
an error, but given how `observeMultiple` works, it is expected that
`_unique` may be `undefined` when navigating away from the Info view.

src/Umbraco.Web.UI.Client/src/packages/documents/documents/workspace/views/info/document-workspace-view-info-links.element.ts

@@ -48,8 +48,7 @@ export class UmbDocumentWorkspaceViewInfoLinksElement extends UmbLitElement {
 
 	async #requestUrls() {
 		if (this._isNew) return;
-
-		if (!this._unique) throw new Error('Document unique is required');
+		if (!this._unique) return;
 
 		const { data } = await this.#documentUrlRepository.requestItems([this._unique]);