Grab-bag of post-feed improvements (#2140)

* Sanity check against cases where empty pages may occur

* Use the mergefeed as an emergency fallback to an empty feed

* Check for new posts on focus

src/view/screens/Home.tsx

@@ -175,7 +175,7 @@ function HomeScreenReady({
         key="1"
         testID="followingFeedPage"
         isPageFocused={selectedPageIndex === 0}
-        feed={homeFeedParams.mergeFeedEnabled ? 'home' : 'following'}
+        feed="home"
         feedParams={homeFeedParams}
         renderEmptyState={renderFollowingEmptyState}
         renderEndOfFeed={FollowingEndOfFeed}