Update export_2d_annotations_as_json.py

[dtransposed]

Since there are tokens in your dataset with contain empty visibility strings, please include them in your default list. Otherwise an user obtains empty .json file. I know that this is just a copy from NuScenes repo, but some people who do not have experience with this API may be super confused.

[jaswanthbjk]

The image size is defaulted in post_process_coords function to 1600*900 in case of nuscenes dataset, But Lyft dataset has two types of images one with 1224 * 1024 and 1920 * 1080

The wrong Image size might cause wrong conversion.