pgsql: Fix nbtree lookahead overflow bug.

Fix nbtree lookahead overflow bug.

Add bounds checking to nbtree's lookahead/skip-within-a-page mechanism.
Otherwise it's possible for cases with lots of before-array-keys tuples
to overflow an int16 variable, causing the mechanism to generate an out
of bounds page offset number.

Oversight in commit 5bf748b8, which enhanced nbtree ScalarArrayOp
execution.

Reported-By: Alexander Lakhin <exclusion@gmail.com>
Discussion: https://postgr.es/m/6c68ac42-bbb5-8b24-103e-af0e279c536f@gmail.com
Backpatch: 17-, where nbtree SAOP execution was enhanced.

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/09a8407dbfd848301cd2c9801c3b4d75adc6cabc

Modified Files
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src/backend/access/nbtree/nbtutils.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)