fixed set current background on a new page

src/core/UBPersistenceManager.cpp

@@ -747,6 +747,11 @@ UBGraphicsScene* UBPersistenceManager::createDocumentSceneAt(UBDocumentProxy* pr
 
     UBGraphicsScene *newScene = mSceneCache.createScene(proxy, index, useUndoRedoStack);
 
+    newScene->setBackground(UBSettings::settings()->isDarkBackground(),
+            UBSettings::settings()->UBSettings::pageBackground());
+
+    newScene->setBackgroundGridSize(UBSettings::settings()->crossSize);
+
     persistDocumentScene(proxy, newScene, index);
 
     proxy->incPageCount();