Unnecessary DB record on host prototype create if inventory mode is disabled

Steps to reproduce:

1. Navigate to Configuration->Templates.
2. Create Discovery rule with Host prototype having "Host inventory" = Disabled.
3. Open table "host_inventory" in any SQL editor and find inventory data of new host prototype by hostid.

Result:
Record is present in DB, "inventory_mode" has value "-1".
Expected:
Record is not present in DB.