The problem with the previous code - which used mp.get_user_path, is
that it returns a path even with --no-config, and even if the file
doesn't exist.
This is why we tested the "config" property, and also used
mp.utils.file_info to check that the file exists.
mp.find_config_file doesn't return a path with no-cofig and doesn't
return a path if the file doesn't exists. It's simpler and better.