Don't crash with 0 byte mails when saving/copying them and trying to add e.g. bodystructure to cache.
Don't crash with 0 byte mails when saving/copying them and trying to add
e.g. bodystructure to cache.

--HG--
branch : HEAD

dscho/dovecot,dscho/dovecot,dscho/dovecot,dscho/dovecot,dscho/dovecot