pgsql: Fixups for commit 93db6cbda0.

Fixups for commit 93db6cbda0.

Ensure to set always-secure search path for both local and remote
connections during slot synchronization, so that malicious users can't
redirect user code (e.g. operators).

In the passing, improve the name of define, remove spurious return
statement, and a minor change in one of the comments.

Author: Bertrand Drouvot and Shveta Malik
Reviewed-by: Amit Kapila, Peter Smith
Discussion: https://postgr.es/m/514f6f2f-6833-4539-39f1-96cd1e011f23@enterprisedb.com
Discussion: https://postgr.es/m/ZdcejBDCr+wlVGnO@ip-10-97-1-34.eu-west-3.compute.internal
Discussion: https://postgr.es/m/CAJpy0uBNP=nrkNJkJSfF=jSocEh8vU2Owa8Rtpi=63fG=SvfVQ@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/b3f6b14cf48ffa81084072f1fdeee2fe9df20746

Modified Files
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src/backend/access/transam/xlogrecovery.c | 15 +++---
.../libpqwalreceiver/libpqwalreceiver.c | 6 ++-
src/backend/replication/logical/slotsync.c | 23 +++++----
.../recovery/t/040_standby_failover_slots_sync.pl | 54 ++++++++++++++++++++++
4 files changed, 82 insertions(+), 16 deletions(-)