def validate_urls(urls):
    """
    Make sure each URL in a list starts with 'http://' and is not empty,
    which can happen when reading URLs from a file.

    :param list(str) urls: list of URLs
    :return list(str): list of validated URLs
    """
    validated = []
    for u in urls:
        if u.startswith('http://'):
            validated.append(u)
        elif u.startswith('www.'):
            validated.append(f'http://{u}')
        else:
            continue
    return validated
