[RFC 2426][1] says:
> The binary data MUST be encoded using the "B" encoding format.
> Long lines of encoded binary data SHOULD BE folded to 75 characters
> using the folding method defined in [MIME-DIR].
That implies that whitespace may occur in binval data and we thus must
be able to parse this correctly.
[1]: https://datatracker.ietf.org/doc/html/rfc2426#section-2.4.1
