Prevent repeated uploads of the same image under the same file name

[whym]

Presumably because of unstable/interrupted network connection, the app produces unwanted identical versions to the same image.

Examples:

https://commons.wikimedia.org/wiki/File:Marstadter_See_-_6.jpeg
https://commons.wikimedia.org/wiki/File:Dresdner_umland_NO_November_2016_-_17.jpeg
https://commons.wikimedia.org/wiki/File:Relic_bibi_ka_alam.jpeg
https://commons.wikimedia.org/wiki/File:Indian_rupee_de_monitisation.jpeg

[neslihanturan]

For long time overrides arent reported. I think this is solved.