Unable to add static dhcp until enable dhcp

I am a complete newbie who has just installed 0.107.2 on both Linux Mint 20 (installed manually via `curl`) and DietPi 8.0.2 (using [their pre-configured version](https://dietpi.com/docs/software/dns_servers/#adguard-home)). In both cases I was bitten by a bug with adding static dhcp leases, because I wanted to have my dhcp server fully configured before I started it.

I expect to be able to add static dhcp leases immediately after installing AdGuardHome for the first time, but instead you get errors in red when you click "Save":
```
Error: control/dhcp/add_static_lease |
Network Error
```

Nothing appeared in the logs.

I discovered, after some trial and error, that this can be fixed by clicking:
* "Check for DHCP Servers"
* "Enable DHCP Server"
* "Disable DHCP Server"

...but a user probably shouldn't have to do that :-)

I assumed that I had done something terribly wrong with my first installation, which is why I tried again with DietPi, because they always have things nicely configured. It would be better if the next person doesn't have to spend the time figuring out that it wasn't something dumb they had done during installation.

Thanks -- it's a great-looking product, and the installation process was *really* impressive.