pgsql: Fix pg_trgm's picksplit function with all-true datums

Fix pg_trgm's picksplit function with all-true datums

The CACHESIGN.sign field is a BITVECP, not a TRGM, so you should not
use GETSIGN() on it. You don't get a compiler warning because the
GETSIGN() macro includes a cast. It resulted in a bogus read beyond
end of buffer, which would cause bad split decisions or a crash if
you're very unlucky.

Reported-by: Mehmet D. INCE <mehmet(at)mehmetince(dot)net>
Backpatch-through: 14
Security: CVE-2026-14678

Branch
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REL_15_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/c7c82a88c312dc6ff626c037ac12846f1d0ca9c4
Author: Heikki Linnakangas <heikki(dot)linnakangas(at)iki(dot)fi>

Modified Files
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contrib/pg_trgm/trgm_gist.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)