Put BodyFormat before setting the body

* src/mail.cpp (Mail::decryptVerify_o, set_body),
(Mail::updateBody_o): But BodyFormat before setting body.

When changing the body format Outlook does a conversion,
for example it applys a linewrap at 72 characters. So long
lines are broken even if they were properly encoded with
a soft linebreak in quoted printable.

• GnuPG-Bug-Id: T4987