Support for waymo monocular task

[Xiangxu-0103]

Hi, for tfrecrod files under testing_3d_camera_only_detection, it will cause an error that 'NoneType' object has no attribute 'data' when saving lidar points. It seems that the tfrecord files do not contain point cloud data.

[Tai-Wang]

Thanks for your kind reminder. We will check this problem and fix it if necessary ASAP.