pgsql: Fix incorrect calculation in BlockRefTableEntryGetBlocks.

Fix incorrect calculation in BlockRefTableEntryGetBlocks.

The previous formula was incorrect in the case where the function's
nblocks argument was a multiple of BLOCKS_PER_CHUNK, which happens
whenever a relation segment file is exactly 512MB or exactly 1GB in
length. In such cases, the formula would calculate a stop_offset of
0 rather than 65536, resulting in modified blocks in the second half
of a 1GB file, or all the modified blocks in a 512MB file, being
omitted from the incremental backup.

Reported off-list by Tomas Vondra and Jakub Wartak.

Discussion: http://postgr.es/m/CA+TgmoYwy_KHp1-5GYNmVa=zdeJWhNH1T0SBmEuvqQNJEHj1Lw@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/55a5ee30cd65886ff0a2e7ffef4ec2816fbec273

Modified Files
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src/common/blkreftable.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)