Steps to replicate the issue (include links if applicable):

1. Visit https://commons.wikimedia.org/wiki/File:BLABLAaaa.srt
2. See "No file by this name exists, but you can upload it."
3. Click the linked word ........................"upload" (it)
4. Fill out the form...

What happens?:

See "Destination filename: (in red) ....srt
Files of this type cannot be uploaded."

What should have happened instead?:

OK, then don't tell the user "but you can upload it."

Software version (skip for WMF-hosted wikis like Wikipedia):

Other information (browser name/version, screenshots, etc.):