The Boostrap DNS servers are ignored on AdGuard Home when resolving the Fallback DNS servers

### Issue URL (Incorrect Blocking)
[http://notapplicable.na](https://adguardteam.github.io/AnonymousRedirect/redirect.html?url=http%3A%2F%2Fnotapplicable.na)
### Comment
> The Boostrap DNS servers are ignored on AdGuard Home when resolving the Fallback DNS servers.
> After an occurrence where the only main Upstream DNS server failed to respond, AdGuard Home then queried to local dnsmasq on OpenWrt to resolve the Fallback servers.
> The local dnsmasq then forwarded the query back to AdGuard Home which blocked the query since the Fallback servers are in a blocklist (to prevent DNS bypass).
> The Bootstrap servers need to be used for Fallback as well.
>

### Screenshots

Screenshot 1


Screenshot 1 with AdGuard disabled


### System configuration

Information | Value
--- | ---
Platform: | AdGuardHome v0.107.61
System version: | OpenWrt Chaos Calmer 15.05.1
Browser: | Not applicable
Filters: | Ad blocking:
AdGuard Base
Custom filters: | HaGeZi's Encrypted DNS/VPN/TOR/Proxy Bypass