Get "empty document detection" working

document.cpp

@@ -29,7 +29,6 @@ TeletextDocument::TeletextDocument()
 	m_description.clear();
 	m_pageFunction = PFLevelOnePage;
 	m_packetCoding = Coding7bit;
-	m_empty = true;
 	m_subPages.push_back(new LevelOnePage);
 	m_currentSubPageIndex = 0;
 	m_undoStack = new QUndoStack(this);
@@ -44,6 +43,15 @@ TeletextDocument::~TeletextDocument()
 		delete(subPage);
 }
 
+bool TeletextDocument::isEmpty() const
+{
+	for (auto &subPage : m_subPages)
+		if (!subPage->isEmpty())
+			return false;
+
+	return true;
+}
+
 /*
 void TeletextDocument::setPageFunction(PageFunctionEnum newPageFunction)
 {