fix: 'link to material request' button not showing any message if no Material Request found (#19064)

erpnext/public/js/controllers/buying.js

@@ -293,7 +293,7 @@ erpnext.buying.BuyingController = erpnext.TransactionController.extend({
 				items: my_items
 			},
 			callback: function(r) {
-				if(!r.message) {
+				if(!r.message || r.message.length == 0) {
 					frappe.throw(__("No pending Material Requests found to link for the given items."))
 				}
 				else {