pgsql: Avoid fetching from an already-terminated plan.

Avoid fetching from an already-terminated plan.

Some plan node types don't react well to being called again after
they've already returned NULL.  PortalRunSelect() has long dealt
with this by calling the executor with NoMovementScanDirection
if it sees that we've already run the portal to the end.  However,
commit ba2c6d6ce overlooked this point, so that persisting an
already-fully-fetched cursor would fail if it had such a plan.

Per report from Tomas Barton.  Back-patch to v11, as the faulty
commit was.  (I've omitted a test case because the type of plan
that causes a problem isn't all that stable.)

Discussion: https://postgr.es/m/CAPV2KRjd=ErgVGbvO2Ty20tKTEZZr6cYsYLxgN_W3eAo9pf5sw@mail.gmail.com

Branch
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REL_14_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/b7056c0a25e545f4c1efcc1e2a6118e4626e377b

Modified Files
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src/backend/commands/portalcmds.c | 18 +++++++++++++++---
1 file changed, 15 insertions(+), 3 deletions(-)