Filename is not parsed correctly

[Markvy]

Suppose the server hands us the following Content-Disposition:

attachment; filename*=UTF-8''file.txt;

Then we should get a filename of "file.txt", but we get no file name at all.

[Theo van Hoesel]

See RFC 8187: Indicating Character Encoding and Language for HTTP Header Field Parameters

[Markvy]

yay!