lib-storage: mailbox_exists() now returns NOSELECT for invalid mailbox names instead of error.
lib-storage: mailbox_exists() now returns NOSELECT for invalid mailbox names instead of error.

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