BUG #3866: Segfault during table update when using convert_from()

The following bug has been logged online:

Bug reference:      3866
Logged by:          Andrew Gilligan
Email address:      andy@tcpd.net
PostgreSQL version: 8.3RC1
Operating system:   FreeBSD 4.11
Description:        Segfault during table update when using convert_from()
Details:

Greetings,

It seems there exists a bug in the way character set conversion
is handled in some circumstances.

Running the test below results in the server (8.3RC1) segfaulting
every time.  I haven't fully explored the extent, but it exists
with (at least) LATIN2 and LATIN9 conversion.

The database and client encoding are both UTF8.

Best regards,
-Andy

-- test case --
test=# CREATE TABLE t (id int, geo text);
CREATE TABLE
test=# INSERT INTO t (id, geo) VALUES (1,
convert_from(decode('50696f74726bf3772c20506f6c616e64','hex'), 'LATIN9'));
INSERT 0 1
test=# UPDATE t SET geo =
convert_from(decode('50696f74726bf3772c20506f6c616e64','hex'), 'LATIN9');
UPDATE 1
-- more than 1 row is needed to trigger the error
test=# INSERT INTO t (id, geo) VALUES (2,
convert_from(decode('50696f74726bf3772c20506f6c616e64','hex'), 'LATIN9'));
INSERT 0 1
test=# UPDATE t SET geo =
convert_from(decode('50696f74726bf3772c20506f6c616e64','hex'), 'LATIN9');
server closed the connection unexpectedly
        This probably means the server terminated abnormally
        before or while processing the request.
The connection to the server was lost. Attempting reset: Failed.
!>