message: get_node_data service: if no ids requested, send back the last node
diff: @@ -2700,9 +2700,12 @@ bool CoreWrapper::getNodeDataCallback(rtabmap_ros::GetNodeData::Request& req, rt
  req.grid?"true":"false",
  req.user_data?"true":"false");
  + if(req.ids.empty() && rtabmap_.getMemory() && rtabmap_.getMemory()->getLastWorkingSignature())
  + {
  + req.ids.push_back(rtabmap_.getMemory()->getLastWorkingSignature()->id());
  + }
  for(size_t i=0; i<req.ids.size(); ++i)
  {
  -
  int id = req.ids[i];
  Signature s = rtabmap_.getSignatureCopy(id, req.images, req.scan, req.user_data, req.grid, true, true);
  