bug: "no top level messages" crash on Zen email loops

[Olly Betts]

On Mon, Mar 19, 2018 at 05:03:21PM -0300, David Bremner wrote:
> I can confirm this reproduces both the xapian-check and the notmuch-show
> error. Olly agrees that whatever notmuch is doing wrong, it shouldn't
> lead to a corrupted database

There was a Xapian bug here, which I fixed on master last week and will
be fixed in 1.4.6.

If changes to a new database which didn't modify the termlist table were
committed, then a disk block which had been allocated to be the root
block in the termlist table was leaked (not used but not on the
freelist of blocks the table can recycle).  This was largely harmless,
except that it was detected by Database::check() and caused an error.

Cheers,
    Olly