Mark seen when unseen only

app/src/main/java/eu/faircode/email/AdapterMessage.java

@@ -564,9 +564,11 @@ public class AdapterMessage extends PagedListAdapter<TupleMessageEx, AdapterMess
                                 if (!message.content)
                                     EntityOperation.queue(db, message, EntityOperation.BODY);
 
+                                if (!message.ui_seen) {
                                     db.message().setMessageUiSeen(message.id, true);
                                     EntityOperation.queue(db, message, EntityOperation.SEEN, true);
                                 }
+                            }
 
                             db.setTransactionSuccessful();
                         } finally {