Fix pinned pane broken after discussion creation

The pane would appear but the page content would not shift to the right because the hasPane className would be missing

js/src/forum/components/DiscussionComposer.js

@@ -101,7 +101,7 @@ export default class DiscussionComposer extends ComposerBody {
       .save(data)
       .then((discussion) => {
         this.composer.hide();
-        app.discussions.refresh({ deferClear: true });
+        app.discussions.refresh();
         m.route.set(app.route.discussion(discussion));
       }, this.loaded.bind(this));
   }

js/src/forum/components/DiscussionPage.tsx

@@ -53,7 +53,9 @@ export default class DiscussionPage<CustomAttrs extends IDiscussionPageAttrs = I
     // page, then we don't want Mithril to redraw the whole page – if it did,
     // then the pane would redraw which would be slow and would cause problems with
     // event handlers.
-    if (app.discussions.hasItems()) {
+    // We will also enable the pane if the discussion list is empty but loading,
+    // because the DiscussionComposer refreshes the list and redirects to the new discussion at the same time.
+    if (app.discussions.hasItems() || app.discussions.isLoading()) {
       app.pane?.enable();
       app.pane?.hide();
     }