fix: Blanket order rate getting changed on converting to order

(cherry picked from commit 9702a65a0f)

erpnext/public/js/controllers/transaction.js

@@ -17,7 +17,7 @@ erpnext.TransactionController = class TransactionController extends erpnext.taxe
 
 			frappe.model.round_floats_in(item, ["rate", "price_list_rate"]);
 
-			if(item.price_list_rate) {
+			if(item.price_list_rate && !item.blanket_order_rate) {
 				if(item.rate > item.price_list_rate && has_margin_field) {
 					// if rate is greater than price_list_rate, set margin
 					// or set discount