pgsql: Fix incorrect block accounting in TID Range Scans

Fix incorrect block accounting in TID Range Scans

heapgettup_advance_block() (or heapgettup() and heapgettup_pagemode() in
versions before v16) would incorrectly decrement rs_numblocks when
advancing to the next block. Ordinarily this was fine, but if the TID
Range scan plan was used by a scrollable cursor and the cursor was fetched
backwards enough to result in another block being required, then
rs_numblocks may have reached 0 prematurely resulting in the scan ending
prematurely.

Reported-by: Jeff Davis <pgsql(at)j-davis(dot)com>
Author: Ewan Young <kdbase(dot)hack(at)gmail(dot)com>
Discussion: https://postgr.es/m/6b50233fcc0f7d6f4845f083777fa9702d9612e4.camel@j-davis.com
Backpatch-through: 14

Branch
------
REL_15_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/cd7d3e129b79ee41c03001550b43b160e10c2f30

Modified Files
--------------
src/backend/access/heap/heapam.c | 48 +++++++++++++++++++++++++-----
src/test/regress/expected/tidrangescan.out | 26 ++++++++++++++++
src/test/regress/sql/tidrangescan.sql | 12 ++++++++
3 files changed, 78 insertions(+), 8 deletions(-)