pgsql: Fix "wrong varnullingrels" for subquery nestloop parameters.

Fix "wrong varnullingrels" for subquery nestloop parameters.

If we apply outer join identity 3 when relation C is a subquery
having lateral references to relation B, then the lateral references
within C continue to bear the original syntactically-correct
varnullingrels marks, but that won't match what is available from
the outer side of the nestloop.  Compensate for that in
process_subquery_nestloop_params().  This is a slightly hacky fix,
but we certainly don't want to re-plan C in toto for each possible
outer join order, so there's not a lot of better alternatives.

Richard Guo and Tom Lane, per report from Markus Winand

Discussion: https://postgr.es/m/DFBB2D25-DE97-49CA-A60E-07C881EA59A7@winand.at

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/bfd332b3fda5c73e28c05b7ba0aac6cf053cdf00

Modified Files
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src/backend/optimizer/plan/setrefs.c     |  8 ++++---
src/backend/optimizer/util/paramassign.c | 36 +++++++++++++++++++++++++-------
src/test/regress/expected/join.out       | 18 ++++++++++++++++
src/test/regress/sql/join.sql            |  7 +++++++
4 files changed, 59 insertions(+), 10 deletions(-)