[lib] Avoid creation new ChatThreadItem unnecessarily in getSearchRes…

…ultsForEmptySearchText

Summary:
In the process of [investigating ENG-5674](https://linear.app/comm/issue/ENG-5674/improve-performance-of-useflattenedchatlistdata#comment-df182f4b), I noticed an issue here. I had implemented a caching layer for `useFlattenedChatListData` so that it would avoid creating a new `ChatThreadItem` when the underlying data for it had not changed in Redux. But the code here was recreating the `ChatThreadItem` on every render anyways, forcing a bunch of components to rerender (and values to be recalculated) unnecessarily.

While I don't have a good long-term solution for ENG-5674 (and I probably won't prioritize it anytime soon), I think it's always best to avoid constructing new objects when the existing object suffices.

Test Plan: Flow

Reviewers: tomek, angelika

Reviewed By: tomek

Differential Revision: https://phab.comm.dev/D13903

lib/shared/thread-utils.js

@@ -1468,6 +1468,9 @@ function getSearchResultsForEmptySearchText(
           threadIsInHome(sidebar.threadInfo) ===
             threadIsInHome(item.threadInfo),
       );
+      if (sidebarsOnlyInSameTab.length === item.sidebars.length) {
+        return item;
+      }
       return {
         ...item,
         sidebars: sidebarsOnlyInSameTab,