bug#48160: Mumi renders huge messages

[Ricardo Wurmus]

This is now fixed with mumi commit
ca4d83865943f2851b07deaf34b026705c46dd41.

The problem here was that the attachment did not come with a
content-disposition header reporting the size of the attachment.  As a
fall back mumi now also looks at the actual size of the message when
determining whether to hide a multipart message part.

-- 
Ricardo