pgsql: Reset properly errno before calling write()

Reset properly errno before calling write()

6cb3372 enforces errno to ENOSPC when less bytes than what is expected
have been written when it is unset, though it forgot to properly reset
errno before doing a system call to write(), causing errno to
potentially come from a previous system call.

Reported-by: Tom Lane
Author: Michael Paquier
Reviewed-by: Tom Lane
Discussion: https://postgr.es/m/31797.1533326676@sss.pgh.pa.us

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/5a23c74b63ec9f63c648f79b13a900c37332ee55

Modified Files
--------------
src/backend/access/heap/rewriteheap.c           | 1 +
src/backend/access/transam/twophase.c           | 1 +
src/backend/replication/logical/origin.c        | 3 +++
src/backend/replication/logical/reorderbuffer.c | 1 +
src/backend/replication/logical/snapbuild.c     | 1 +
src/backend/replication/slot.c                  | 1 +
src/bin/pg_basebackup/walmethods.c              | 6 ++++++
7 files changed, 14 insertions(+)