pgsql: C comment: mention why no setting lasterrno in dir_existsfile()

C comment: mention why no setting lasterrno in dir_existsfile()

Reported-by: Wei Sun

Discussion: /messages/by-id/tencent_1276C08F98579CC19D8A4488C848A8411806@qq.com

Backpatch-through: master

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/3fdc1d269345cac24275613f4d6b799e195d95a0

Modified Files
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src/bin/pg_basebackup/walmethods.c | 5 +++++
1 file changed, 5 insertions(+)