nodeSetOp.c: missing additionalsize for BuildTupleHashTable().

Provide additionalsize argument, which can affect the calculations for
'nbuckets'. Also, future work for Hash Aggregation will rely on the
correct additionalsize.

Discussion: https://postgr.es/m/7530bd8783b1a78d53a3c70383e38d8da0a5ffe5.camel%40j-davis.com

src/backend/executor/nodeSetOp.c

@@ -104,7 +104,7 @@ build_hash_table(SetOpState *setopstate)
 												setopstate->hashfunctions,
 												node->cmpCollations,
 												node->numGroups,
-												0,
+												sizeof(SetOpStatePerGroupData),
 												setopstate->ps.state->es_query_cxt,
 												setopstate->tableContext,
 												econtext->ecxt_per_tuple_memory,