fix: get incoming rate only if not return

(cherry picked from commit fcc885bc16)

erpnext/controllers/selling_controller.py

@@ -385,7 +385,7 @@ class SellingController(StockController):
 				# Get incoming rate based on original item cost based on valuation method
 				qty = flt(d.get('stock_qty') or d.get('actual_qty'))
 
-				if not d.incoming_rate:
+				if not (self.get("is_return") and d.incoming_rate):
 					d.incoming_rate = get_incoming_rate({
 						"item_code": d.item_code,
 						"warehouse": d.warehouse,