Repair commit b81b5a96f4.

This commit purported to use a variable hash seed for Partial
HashAggregate, but actually did the opposite - it made us use a
variable seed for any HashAggregate that is NOT partial.  Woops.

src/backend/executor/nodeAgg.c

@@ -1738,7 +1738,7 @@ build_hash_table(AggState *aggstate)
 											  additionalsize,
 							 aggstate->aggcontexts[0]->ecxt_per_tuple_memory,
 											  tmpmem,
-								  !DO_AGGSPLIT_SKIPFINAL(aggstate->aggsplit));
+								  DO_AGGSPLIT_SKIPFINAL(aggstate->aggsplit));
 }
 
 /*