pgsql: Guard against zero vardata.rel->tuples in estimate_hash_bucketsi

Guard against zero vardata.rel->tuples in estimate_hash_bucketsize().

If the referenced rel was proven empty, we'd compute 0/0 here, which
results in the function returning NaN.  That's a bit more serious
than the other zero-divide case.  Still, it only seems to be possible
in HEAD, so no back-patch.

Per report from Piotr Stefaniak.  I looked through the rest of selfuncs.c
and found no other likely trouble spots.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/d65b665d524a67273b075f468bf3d60ce31f4040

Modified Files
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src/backend/utils/adt/selfuncs.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)