Support loading single content events

Handles the case where the root of a publication tree is identical to its one and only leaf, i.e., the publication consists of a single event.

src/lib/components/Publication.svelte

@@ -39,7 +39,7 @@
 
     for (let i = 0; i < count; i++) {
       const nextItem = await publicationTree.next();
-      if (leaves.includes(nextItem.value) || nextItem.done) {
+      if (leaves.includes(nextItem.value) || (nextItem.done && nextItem.value === null)) {
         isLoading = false;
         return;
       }

src/lib/data_structures/publication_tree.ts

@@ -4,7 +4,6 @@ import { Lazy } from "./lazy.ts";
 import { findIndexAsync as _findIndexAsync } from '../utils.ts';
 
 enum PublicationTreeNodeType {
-  Root,
   Branch,
   Leaf,
 }
@@ -50,7 +49,7 @@ export class PublicationTree implements AsyncIterable<NDKEvent> {
   constructor(rootEvent: NDKEvent, ndk: NDK) {
     const rootAddress = rootEvent.tagAddress();
     this.#root = {
-      type: PublicationTreeNodeType.Root,
+      type: this.#getNodeType(rootEvent),
       address: rootAddress,
       children: [],
     };
@@ -286,9 +285,15 @@ export class PublicationTree implements AsyncIterable<NDKEvent> {
         continue;
       }
 
-      if (this.#cursor.target?.type === PublicationTreeNodeType.Root) {
+      const isRoot = this.#cursor.target?.address === this.#root.address;
+
+      if (isRoot && this.#cursor.target?.type === PublicationTreeNodeType.Branch) {
         return { done: true, value: null };
       }
+
+      if (isRoot && this.#cursor.target?.type === PublicationTreeNodeType.Leaf) {
+        return { done: true, value: this.#events.get(this.#cursor.target!.address)! };
+      }
     } while (this.#cursor.target?.type !== PublicationTreeNodeType.Leaf);
 
     const event = await this.getEvent(this.#cursor.target!.address);
@@ -414,11 +419,7 @@ export class PublicationTree implements AsyncIterable<NDKEvent> {
     return node;
   }
 
-  async #getNodeType(event: NDKEvent): Promise<PublicationTreeNodeType> {
-    if (event.tagAddress() === this.#root.address) {
-      return PublicationTreeNodeType.Root;
-    }
-
+  #getNodeType(event: NDKEvent): PublicationTreeNodeType {
     if (event.kind === 30040 && event.tags.some(tag => tag[0] === 'a')) {
       return PublicationTreeNodeType.Branch;
     }