pgsql: Use consistent style for checking return from system calls

Use consistent style for checking return from system calls

Use

if (something() != 0)
error ...

instead of just

if (something)
error ...

The latter is not incorrect, but it's a bit confusing and not the
common style.

Discussion: https://www.postgresql.org/message-id/flat/5de61b6b-8be9-7771-0048-860328efe027%402ndquadrant.com

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/7e9a4c5c3dca0d9637812d8991e96fc8f46800d9

Modified Files
--------------
contrib/pg_stat_statements/pg_stat_statements.c | 2 +-
src/backend/access/heap/rewriteheap.c | 4 ++--
src/backend/access/transam/slru.c | 12 ++++++------
src/backend/access/transam/timeline.c | 6 +++---
src/backend/access/transam/twophase.c | 2 +-
src/backend/access/transam/xlog.c | 14 +++++++-------
src/backend/libpq/be-fsstubs.c | 4 ++--
src/backend/postmaster/postmaster.c | 2 +-
src/backend/replication/logical/origin.c | 4 ++--
src/backend/replication/logical/reorderbuffer.c | 2 +-
src/backend/replication/logical/snapbuild.c | 4 ++--
src/backend/replication/slot.c | 4 ++--
src/backend/replication/walsender.c | 2 +-
src/backend/storage/file/copydir.c | 4 ++--
src/backend/storage/file/fd.c | 10 +++++-----
src/backend/storage/ipc/dsm_impl.c | 2 +-
src/backend/utils/cache/relmapper.c | 4 ++--
src/common/controldata_utils.c | 6 +++---
src/interfaces/libpq/fe-lobj.c | 2 +-
19 files changed, 45 insertions(+), 45 deletions(-)