"Picture too dark" warning when uploading an OGG file

[jidanni]

I uploaded this fine, https://commons.wikimedia.org/wiki/File%3A%E5%8F%B0%E7%81%A3%E5%8F%B0%E4%B8%AD%E6%9D%B1%E5%8B%A2%E7%95%AB%E7%9C%89.ogg
But during the process I got a warning that my "picture was too dark". It's not a picture at all. It's an OGG file!

[neslihanturan]

~~Oh, I will create an issue for this. Thanks a lot for your feedback.~~ Well, you have already created it thanks :) Additionally test codes should be added in scope of this PR.