fix: get_items from product bundle for purchase order (#22821)

* fix: get_items from product bundle for purchase order

* fix: Don't overwrite  doctype while setting attributes in child row

Co-authored-by: Marica <maricadsouza221197@gmail.com>
diff --git a/erpnext/public/js/controllers/buying.js b/erpnext/public/js/controllers/buying.js
index a4cc68b..cb76c87 100644
--- a/erpnext/public/js/controllers/buying.js
+++ b/erpnext/public/js/controllers/buying.js
@@ -503,11 +503,11 @@
 
 					if(!r.exc && r.message) {
 						remove_empty_first_row(frm);
-						for ( var i=0; i< r.message.length; i++ ) {
+						for (var i=0; i< r.message.length; i++) {
 							var d = frm.add_child("items");
 							var item = r.message[i];
-							for ( var key in  item) {
-								if ( !is_null(item[key]) ) {
+							for (var key in  item) {
+								if (!is_null(item[key]) && key !== "doctype") {
 									d[key] = item[key];
 								}
 							}