pgsql: Fix assorted infelicities in new SetWALSegSize() function.

Fix assorted infelicities in new SetWALSegSize() function.

* Failure to check for malloc failure (ok, pretty unlikely here, but
that's not an excuse).

* Leakage of open fd on read error, and of malloc'd buffer always.

* Incorrect assumption that a short read would set errno to zero.

* Failure to adhere to message style conventions (in particular,
not reporting errno where relevant; using "couldn't open" rather than
"could not open" is not really in line with project style either).

* Missing newlines on some messages.

Coverity spotted the leak problems; I noticed the rest while
fixing the leaks.

Branch
------
master

Details
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https://git.postgresql.org/pg/commitdiff/8485a25a8c9a419ff3e0d30e43e4abd5e680cc65

Modified Files
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contrib/pg_standby/pg_standby.c | 20 ++++++++++++++------
1 file changed, 14 insertions(+), 6 deletions(-)