dbox: Don't try to finish saving attachments if saving has already failed. Fixes an assert crash with failed CATENATE.
dbox: Don't try to finish saving attachments if saving has already failed.
Fixes an assert crash with failed CATENATE.

damoxc/dovecot,damoxc/dovecot,damoxc/dovecot,damoxc/dovecot,damoxc/dovecot