Fix goToIndex to visible end

In the PostStream, `this.visibleEnd` represents the index of the last post + 1, but `loadNearIndex` treated it as if it was the index of the last post. This means that executing `goToIndex` on the post stream's current `this.visiblePost` didn't load new posts, and as a result, the requested scrolling did not occur.

js/src/forum/states/PostStreamState.js

@@ -172,7 +172,7 @@ class PostStreamState {
    * @return {Promise}
    */
   loadNearIndex(index) {
-    if (index >= this.visibleStart && index <= this.visibleEnd) {
+    if (index >= this.visibleStart && index < this.visibleEnd) {
       return Promise.resolve();
     }