Do not upload duplicate file

[jaroslaw Tuszynski]

https://commons.wikimedia.org/wiki/File:March_For_Our_Lives_2018_-San_Francisco(3216)(27130570028).jpg was uploaded using flickr2commons 3 days after https://commons.wikimedia.org/wiki/File:March_For_Our_Lives_2018-San_Francisco(3216).jpg upload. Together with few hundred other files. I thought all upload tools prevent duplicate file uploads, but flickr2commons must be an exception.