pgsql: Don't assume that PageIsEmpty() returns true on an all-zeros pag

Don't assume that PageIsEmpty() returns true on an all-zeros page.

It does currently, and I don't see us changing that any time soon, but we
don't make that assumption anywhere else.

Per Tom Lane's suggestion. Backpatch to 9.2, like the previous patch that
added this assumption.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/820d1ced1b308702b3f811647810b4030f974d89

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