Don't crash if transaction log contains records for messages that don't exist anymore.
Don't crash if transaction log contains records for messages that don't
exist anymore.

--HG--
branch : HEAD

dscho/dovecot,dscho/dovecot,jwm/dovecot-notmuch,jwm/dovecot-notmuch,jkerihuel/dovecot,jkerihuel/dovecot,jkerihuel/dovecot,jwm/dovecot-notmuch,jkerihuel/dovecot,dscho/dovecot,dscho/dovecot,jkerihuel/dovecot,dscho/dovecot,jwm/dovecot-notmuch,jwm/dovecot-notmuch