BRODEN dataset, scene number 0

Hey,

While using your method and BRODEN dataset, I've seen that some images have an associated scene number of `0`. This scene number is not defined in `c_scene.csv`. When checking some images, e.g., `"ade20k/ADE_train_00015917.jpg"`, `"ade20k/ADE_train_00008543.jpg"`, `"ade20k/ADE_train_00002038.jpg"`, I couldn't see any common scene description.

The only reference I've found to a scene number `0` would be in `sync.txt` but I don't know what this means.

Could it be possible that the scene number `0` is a mistake? I just found it because this lead to issues later on in the code, e.g., generating a HTML summary with missing labels.

Thanks :)