[minor] don't trigger source_warehouse if item_code is not set in Production Order (#9806)

diff --git a/erpnext/manufacturing/doctype/production_order/production_order.js b/erpnext/manufacturing/doctype/production_order/production_order.js
index f6d9eaf..657819a 100644
--- a/erpnext/manufacturing/doctype/production_order/production_order.js
+++ b/erpnext/manufacturing/doctype/production_order/production_order.js
@@ -212,7 +212,9 @@
 frappe.ui.form.on("Production Order Item", {
 	source_warehouse: function(frm, cdt, cdn) {
 		var row = locals[cdt][cdn];
-		if(row.source_warehouse) {
+		if(!row.item_code) {
+			frappe.throw(__("Please set the Item Code first"));
+		} else if(row.source_warehouse) {
 			frappe.call({
 				"method": "erpnext.stock.utils.get_latest_stock_qty",
 				args: {