Since we're getting pretty close to the next set of back-branch releases,
I went ahead and pushed a minimal fix along the lines suggested by Shi Yu.
(I realized that there's a second ExecFindPartition call in worker.c that
also needs a check.) We still can at leisure think about refactoring
CheckSubscriptionRelkind to avoid unnecessary lookups. I think that
is something we should do only in HEAD; it'll just be a marginal savings,
not worth the risks of API changes in stable branches. The other loose
end is whether to worry about a regression test case. I'm inclined not
to bother. The only thing that isn't getting exercised is the actual
ereport, which probably isn't in great need of routine testing.
regards, tom lane