pgsql: During repeated rescan of GiST index it's possible that scan key

Log Message:
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During repeated rescan of GiST index it's possible that scan key
is NULL but SK_SEARCHNULL is not set. Add checking IS NULL of keys
to set during key initialization. If key is NULL and SK_SEARCHNULL is not
set then nothnig can be satisfied.
With assert-enabled compilation that causes coredump.

Bug was introduced in 8.3 by support of IS NULL index scan.

Tags:
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REL8_3_STABLE

Modified Files:
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pgsql/src/backend/access/gist:
gistget.c (r1.69.2.1 -> r1.69.2.2)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/gist/gistget.c?r1=1.69.2.1&r2=1.69.2.2)
gistscan.c (r1.68.2.1 -> r1.68.2.2)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/gist/gistscan.c?r1=1.68.2.1&r2=1.68.2.2)
pgsql/src/include/access:
gist_private.h (r1.28.2.1 -> r1.28.2.2)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/access/gist_private.h?r1=1.28.2.1&r2=1.28.2.2)