fix: assume parentfield to be set and valid

(cherry picked from commit 7183efa60d)

frappe/permissions.py

@@ -706,7 +706,6 @@ def has_child_table_permission(
 
 	if (
 		child_doc
-		and child_doc.parentfield
 		and (permlevel := parent_meta.get_field(child_doc.parentfield).permlevel) > 0
 		and permlevel not in parent_meta.get_permlevel_access(ptype)
 	):