view: try assuming UTF-8 for bogus charsets

view: try assuming UTF-8 for bogus charsets

For some reason, Alpine will set X-UNKNOWN for valid UTF-8.
Since we favor UTF-8 HTML anyways, try forcing Email::MIME to
handle text/plain as UTF-8 which might show up better.

At least this change renders

	<alpine.DEB.2.20.1608131214070.4924@virtualbox>

properly by showing "•" (&#8226;) instead of
"â ¢" (&#226;&#128;&#162;)

Reported-by: Thomas Ferris Nicolaisen <tfnico@gmail.com>