lib-index: Replaced ext-header update assert with "index corrupted" error handling.
lib-index: Replaced ext-header update assert with "index corrupted" error handling.

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