Fix reading inline-ciphertext in multipart/alternative-messages
Currently we/mail-gpg hands the HTML-wrapped ciphertext to gpgme (because "-----BEGIN PGP MESSAGE-----" is found inside of the body), which chokes (GPGME::Error::NoData).
Upstream bug-report with mail-gpg: https://github.com/jkraemer/mail-gpg/issues/49
One possible solution would be to strip the html-part from multi/alt-messages if ciphertext is found inside. Then we can handle the text-part properly. See #90 (closed)