Don't reset library adapter if it's not needed

app/src/main/java/eu/kanade/tachiyomi/ui/library/LibraryAdapter.java

@@ -32,8 +32,10 @@ public class LibraryAdapter extends SmartFragmentStatePagerAdapter {
     }
 
     public void setCategories(List<Category> categories) {
-        this.categories = categories;
-        notifyDataSetChanged();
+        if (this.categories != categories) {
+            this.categories = categories;
+            notifyDataSetChanged();
+        }
     }
 
     public void setSelectionMode(int mode) {

app/src/main/java/eu/kanade/tachiyomi/ui/library/LibraryCategoryFragment.java

@@ -34,6 +34,7 @@ public class LibraryCategoryFragment extends BaseFragment
 
     @State int position;
     private LibraryCategoryAdapter adapter;
+    private List<Manga> mangas;
 
     private Subscription numColumnsSubscription;
 
@@ -112,10 +113,13 @@ public class LibraryCategoryFragment extends BaseFragment
 
         Category category = categories.get(position);
         List<Manga> mangas = event.getMangasForCategory(category);
-        if (mangas == null) {
-            mangas = new ArrayList<>();
+        if (this.mangas != mangas) {
+            this.mangas = mangas;
+            if (mangas == null) {
+                mangas = new ArrayList<>();
+            }
+            setMangas(mangas);
         }
-        setMangas(mangas);
     }
 
     protected void openManga(Manga manga) {