Reseller's Mail Quota Limit ignored when creating customers

When the admin user creates a reseller with a fixed Mail Quota limit and that reseller creates a client he can assign a mail quota of -1 giving that client the possibility to bypass the mail quota limit for the reseller.

Expected behaivior: When creating a customer, check (max_allowed_quota = reseller_allowed_quota - reseller_mailboxes_allocated_quota - reseller_allocated_existing_client_quota)