pgsql: Correct handling of fsync failures with tar mode ofwalmethods.c

Correct handling of fsync failures with tar mode of walmethods.c

This file has been missing the fact that it needs to report back to
callers a proper failure on fsync calls.  I have spotted the one in
tar_finish() while Kuntal has spotted the one in tar_close().

Backpatch down to 10 where this code has been introduced.

Reported by: Michael Paquier, Kuntal Ghosh
Author: Michael Paquier
Reviewed-by: Kuntal Ghosh, Magnus Hagander
Discussion: https://postgr.es/m/20180625024356.GD1146@paquier.xyz

Branch
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REL_10_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/324076a6261756d6f5b3514ed2b2f715b656ba90

Modified Files
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src/bin/pg_basebackup/walmethods.c | 10 +++++++---
1 file changed, 7 insertions(+), 3 deletions(-)