pgsql: pg_checksums: Handle read and write returns correctly

pg_checksums: Handle read and write returns correctly

The read() return was not checking for errors, the write() return was
not checking for short writes.

Reviewed-by: Michael Paquier <michael@paquier.xyz>
Discussion: https://www.postgresql.org/message-id/flat/5de61b6b-8be9-7771-0048-860328efe027%402ndquadrant.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/1d7a6e3eb45946db86d6d1776c55323740d955b0

Modified Files
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src/bin/pg_checksums/pg_checksums.c | 21 ++++++++++++++++-----
1 file changed, 16 insertions(+), 5 deletions(-)