dbox: Added a sanity check so that too small dbox files won't be appended to.
dbox: Added a sanity check so that too small dbox files won't be appended to.

LTD-Beget/dovecot,LTD-Beget/dovecot,LTD-Beget/dovecot,LTD-Beget/dovecot,LTD-Beget/dovecot