null check to avoid launch crash

immediately hitting the feed tab after launch will produce the following crash, so this resolves it by a null check:

```
java.lang.NullPointerException: Attempt to read from field 'awais.instagrabber.customviews.PostsRecyclerView awais.instagrabber.databinding.FragmentFeedBinding.feedRecyclerView' on a null object reference
	at awais.instagrabber.fragments.main.FeedFragment.scrollToTop(FeedFragment.java:461)
	at awais.instagrabber.utils.NavigationExtensions.lambda$setupItemReselected$2(NavigationExtensions.java:190)
	at awais.instagrabber.utils.-$$Lambda$NavigationExtensions$C3II1R-NOFB80ERAxio06uf3Qto.onNavigationItemReselected(Unknown Source:4)
...
```

app/src/main/java/awais/instagrabber/fragments/main/FeedFragment.java

@@ -458,8 +458,10 @@ public class FeedFragment extends Fragment implements SwipeRefreshLayout.OnRefre
     }
 
     public void scrollToTop() {
-        binding.feedRecyclerView.smoothScrollToPosition(0);
-        // binding.storiesContainer.setExpanded(true);
+        if (binding != null) {
+            binding.feedRecyclerView.smoothScrollToPosition(0);
+            // binding.storiesContainer.setExpanded(true);
+        }
     }
 
     private boolean isSafeToNavigate(final NavController navController) {