free resources on app destruction

src/node_canvas.cpp

@@ -523,3 +523,14 @@ void NodeCanvas::reset_camera()
     m_canvas->m_cam_fov = 85;
     m_canvas->m_pan = {0, 0};
 }
+
+void NodeCanvas::destroy_immediate()
+{
+    Node::destroy_immediate();
+    m_blender_rtt.destroy();
+    m_cache_rtt.destroy();
+    m_blender_bg.destroy();
+    m_face_plane.destroy();
+    m_line.destroy();
+    m_grid.destroy();
+}