lib-storage: Don't crash if INBOX is in a namespace with non-"" non-"INBOX/" prefix.
lib-storage: Don't crash if INBOX is in a namespace with non-"" non-"INBOX/" prefix.

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