lmtp proxy: Don't crash if all RCPT TOs fail to a remote.
lmtp proxy: Don't crash if all RCPT TOs fail to a remote.

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