set default params for paging (#11500)

diff --git a/erpnext/controllers/queries.py b/erpnext/controllers/queries.py
index b1618d5..37afed7 100644
--- a/erpnext/controllers/queries.py
+++ b/erpnext/controllers/queries.py
@@ -185,7 +185,7 @@
 				"page_len": page_len
 			}, as_dict=as_dict)
 
-def bom(doctype, txt, searchfield, start, page_len, filters):
+def bom(doctype, txt, searchfield, filters, start=0, page_len=20):
 	conditions = []
 
 	return frappe.db.sql("""select tabBOM.name, tabBOM.item