pgsql: Fix another instance of unsafe coding for shm_toc_lookupfailure

Fix another instance of unsafe coding for shm_toc_lookup failure.

One or another author of commit 5bcf389ec seems to have thought that
computing an offset from a NULL pointer would yield another NULL pointer.
There may possibly be architectures where that works, but common machines
don't work like that.  Per a quick code review of places calling
shm_toc_lookup and not using noError = false.

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/d59ff4ab3111f20054425d82dab1393101dcfe8e

Modified Files
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src/backend/executor/nodeHash.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)