pgsql: Don't use elog() in src/port/pwrite.c.

Don't use elog() in src/port/pwrite.c.

Nothing broke because of this oversight yet, but it would fail to link
if we tried to use pg_pwrite() in frontend code on a system that lacks
pwrite().  Use an assertion instead.  Also pgindent while here.

Discussion: https://postgr.es/m/CA%2BhUKGL57RvoQsS35TVPnQoPYqbtBixsdRhynB8NpcUKpHTTtg%40mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/df10ac625c1672edf839ff59cfcac9dcc097515c

Modified Files
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src/port/pwrite.c | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)