implement shading modes switch for heightmap

src/node_combobox.cpp

@@ -19,6 +19,8 @@ void NodeComboBox::clone_copy(Node* dest) const
 void NodeComboBox::loaded()
 {
     NodeButton::loaded();
+    m_text->set_text(m_data[m_current_index].c_str());
+    m_selected_child_index = m_current_index;
     on_click = [this](Node* target) {
         NodePopupMenu* popup = new NodePopupMenu;
         popup->init();