pgsql: Fix limit block handling in pg_wal_summary_contents().

Fix limit block handling in pg_wal_summary_contents().

Previously, pg_wal_summary_contents() had two issues,
causing discrepancies between pg_wal_summary_contents()
and the pg_walsummary command on the same WAL summary file:

(1) It did not emit the limit block when that's the only data for
a particular relation fork.
(2) It emitted the same limit block multiple times if the list of
block numbers was long enough.

This commit fixes these issues.

Backpatch to v17 where pg_wal_summary_contents() was added.

Author: Fujii Masao
Reviewed-by: Robert Haas
Discussion: https://postgr.es/m/90980ee6-2da6-42f6-a7b0-b7bae62ae279@oss.nttdata.com

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/c8d5d6c78af4a55c5c36e2fa8e73d1f2b2e9d777

Modified Files
--------------
src/backend/backup/walsummaryfuncs.c | 34 +++++++++++++++++-----------------
1 file changed, 17 insertions(+), 17 deletions(-)