Header fields with unencoded Unicode characters incorrectly displayed

[octo]

This ticket is probably the result of some E-Mail sending application violating the message header specifications, though it still needs to be dealt with.

Normally, any message header value that isn't US-ASCII is supposed to be encoded according to RFC2047 in a special format that uses quoted-printable or base64.

However, it has been reported here that sometimes messages are sent with raw Unicode (most likely UTF-8) in their headers. This currently fails to display correctly. As a sanity check, I've confirmed that Thunderbird does correctly display these headers.

The solution will likely involve reinterpreting the header text bytes as a UTF-8 string somewhere in the parsing sequence.