Fixed PERCENT_RANK computation (#8972)

Author: sim1984

src/dsql/WinNodes.cpp

@@ -259,12 +259,12 @@ dsc* PercentRankWinNode::winPass(thread_db* /*tdbb*/, jrd_req* request, SlidingW
 	impure_value_ex* impure = request->getImpure<impure_value_ex>(impureOffset);
 	impure_value_ex* impureTemp = request->getImpure<impure_value_ex>(tempImpure);
 
-	const double partitionSize = window->getPartitionSize();
-	const double divisor = (partitionSize - 1) * (impureTemp->vlux_count - 1);
+	const double dividend = impureTemp->vlux_count - 1;
+	const double divisor = window->getPartitionSize() - 1;
 
 	impureTemp->vlu_misc.vlu_double = divisor == 0 ?
 		0 :
-		1 / divisor;
+		dividend / divisor;
 
 	return &impureTemp->vlu_desc;
 }