ParseMediaType tolerates unencoded 8bit characters

[pavelbazika]

Hi,

I'm here with yet another RFC violation tolerance pull request.

Some emails does not encode mime param with RFC 2047 encoding when they should. I.e when there are some characters with unicode value out of US-ASCII (> 127). Namely a chinese client Foxmail created such emails at least in the past.

I've improved the function consumeParam used by fixUnquotedSpecials to check for such violation and when it occurs, it encodes the value with RFC 2017.

It's expected that the bytes are in UTF-8 encoding, but when not, the invalid bytes are encoded to base64 too. As a result,. ReadEnvelope does not end with error when an email with wrongly encoded attachment part is parsed and at least something (headers, body) is readable.

[jhillyerd]

Nice work, couple change requests. Can we also add a single test for ReadEnvelope as well to prevent future changes from defeating this fix?

[jhillyerd]

Thanks!