[Dovecot] those assertions

[dovecot at spam.turbolink.net]

Timo,

Just FYI while you're working on the mbox code, I discovered a bug that
occasionally causes dovecot to insert a single blank line at the beginning
of the mbox, I'm not sure when/how/why.

A single blank line seems to really confuse dovecot, and causes the server
to crash when somebody connects to an afflicted mbox.  ("Error indexing
mbox" in the log, and disconects the user right away).

I fixed it with lots of ugly code at our site (basically just remember
that we skipped an intial blank line when doing other operations, instead
of skipping it then forgetting later).  I suspect there's a more elegant
way to do it.

- Mike