update_database.py occasionally fails

[DanielRJohnson]

Some days, update_database.py fails as follows:

for vid in videos:
        for chapter in vid["chapters"] if vid["chapters"] else []:
                # vid is None, vid["chapters"] throws an error

Probably just needs a "if vid is None: continue", but not sure why vid can be None in the first place and only is None on occasion.