Fix item decoration add/remove logic and one null check

app/src/main/java/awais/instagrabber/customviews/PostsRecyclerView.java

@@ -216,6 +216,7 @@ public class PostsRecyclerView extends RecyclerView {
                            if (progressPercent != 100) continue;
                            final String url = progress.getString(DownloadWorker.URL);
                            final List<FeedModel> feedModels = feedViewModel.getList().getValue();
+                           if (feedModels == null) continue;
                            for (int i = 0; i < feedModels.size(); i++) {
                                final FeedModel feedModel = feedModels.get(i);
                                final List<String> displayUrls = getDisplayUrl(feedModel);
@@ -254,10 +255,15 @@ public class PostsRecyclerView extends RecyclerView {
         post(() -> {
             TransitionManager.beginDelayedTransition(this, transition);
             feedAdapter.notifyDataSetChanged();
+            final int itemDecorationCount = getItemDecorationCount();
             if (!layoutPreferences.getHasGap()) {
-                removeItemDecoration(gridSpacingItemDecoration);
+                if (itemDecorationCount == 1) {
+                    removeItemDecoration(gridSpacingItemDecoration);
+                }
             } else {
-                addItemDecoration(gridSpacingItemDecoration);
+                if (itemDecorationCount == 0) {
+                    addItemDecoration(gridSpacingItemDecoration);
+                }
             }
             if (layoutPreferences.getType() == PostsLayoutPreferences.PostsLayoutType.LINEAR) {
                 if (layoutManager.getSpanCount() != 1) {