pgsql: Fix masking of SP-GiST pages during xlog consistency check

Fix masking of SP-GiST pages during xlog consistency check

spg_mask() didn't take into account that pd_lower equal to SizeOfPageHeaderData
is still valid value.  This commit fixes that.  Backpatch to 11, where
spg_mask() pg_lower check was introduced.

Reported-by: Michael Paquier
Discussion: https://postgr.es/m/20200615131405.GM52676%40paquier.xyz
Backpatch-through: 11

Branch
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REL_11_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/3f88e2d78dbe61b8eec8dfb051b9dc0d1ff0052f

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