stupid subselect core dumps

I know this is too simple to be useful, but it was the first test case I
tried for a regression test :)

regression=> SELECT 1 AS one WHERE 1 IN (SELECT 1);
PQexec() -- Request was sent to backend, but backend closed the channel
before responding.
        This probably means the backend terminated abnormally before or
while processing the request.

Should we disallow parts of this in or near the parser, or can the
backend possibly handle it?

                                                   - Tom