It could and does, as quoted in my original report.

Content-Type: text/plain; charset*=utf-8”''utf-8%E2%80%9D

That’s a U+201D right double quotation mark.

This is not a valid charset for the charset of course, but it seems like the code was intended to handle an invalid charset value without crashing, so it should also handle an invalid charset charset (despite the absurdity of the entire concept of a charset charset).