use.system.public.ips does nothing when domain doesn't have a range

##### ISSUE TYPE

* Bug Report

##### COMPONENT NAME

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IP assignment
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##### CLOUDSTACK VERSION

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4.17,
4.18,
main (*)
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(*): Although I didn't test that on main branch, the code pard didn't change so it should be there as well.

##### SUMMARY

By default when user use all of their assigned public IPs, they can use system public IPs. Although by using the `use.system.public.ips` setting admins can prevent that action, the setting doesn't have any affect when user doesn't have any reserved range.

##### STEPS TO REPRODUCE

1. Login as a `root admin`
2. Create a domain and a domain admin account for the domain.
3. Set `use.system.public.ips` to `false` in the account, the domain or globally.
4. Assign an IP range to the domain or the account. `[Range 1]`
5. Login as a `domain admin` and create an isolated network in domain.
6. Go to the isolated network page and click on the `Public IP addresses` then click on `Acquire new IP`.
7. The list shows only the IPs in the assinged IP range `[Range 1]`
8. Logout and login as a `root admin` again
9. Remove the `[Range1]` IP range assignment.
10. Repeat step `5`, `6`, and `7`. The output list now includes the system IPs.

##### EXPECTED RESULTS

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User can NOT see the system's public IP addresses.
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##### ACTUAL RESULTS

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User can see the system's public IP addresses.
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