[Dovecot] segfault in RC15

[Cor Bosman]

> See if this patch makes it give corrupted index file errors instead:
> 
> http://dovecot.org/list/dovecot-cvs/2006-December/007059.html

It does:

Dec 10 18:55:44 dovecot2.xs4all.nl dovecot: IMAP(XXX): Corrupted Index file /var/run/dovecot-index/l/ld/XXX/.INBOX/dovecot.index: Record [27].uid=0
Dec 10 20:07:28 dovecot2.xs4all.nl dovecot: IMAP(XXX): Corrupted Index file /var/run/dovecot-index/d/di/XXX/.INBOX/dovecot.index: Record [1659].uid=0
Dec 10 20:07:33 dovecot2.xs4all.nl dovecot: IMAP(XXX): Corrupted Index file /var/run/dovecot-index/d/di/XXX/.INBOX/dovecot.index: Record [1659].uid=0


Cor