pgsql: Fix "wrong varnullingrels" for Memoize's lateral references, too

Fix "wrong varnullingrels" for Memoize's lateral references, too.

The issue fixed in commit bfd332b3f can also bite Memoize plans,
because of the separate copies of lateral reference Vars made
by paraminfo_get_equal_hashops.  Apply the same hacky fix there.

(In passing, clean up shaky grammar in the existing comments
for this function.)

Richard Guo

Discussion: https://postgr.es/m/CAMbWs4-krwk0Wbd6WdufMAupuou_Ua73ijQ4XQCr1Mb5BaVtKQ@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/63e4f13d2a78124c798165814a679b0534db87a5

Modified Files
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src/backend/optimizer/path/joinpath.c | 55 ++++++++++++++++++++++++++++++-----
src/backend/optimizer/plan/setrefs.c  | 10 +++----
src/test/regress/expected/join.out    | 21 +++++++++++++
src/test/regress/sql/join.sql         |  7 +++++
4 files changed, 81 insertions(+), 12 deletions(-)