fixed an issue where reload thumbnails would be called twice with the second call not using the good source container

src/document/UBDocumentController.cpp

@@ -3217,7 +3217,6 @@ void UBDocumentController::addToDocument()
         UBMetadataDcSubsetAdaptor::persist(mBoardController->selectedDocument());
         mBoardController->reloadThumbnails();
 
-        emit mBoardController->documentThumbnailsUpdated(this);
         UBApplication::applicationController->showBoard();
 
         mBoardController->setActiveDocumentScene(newActiveSceneIndex);