Fallback upstream is not activated for invalid plain dns upstream

[Versty]

Version

AdGuard for Android 4.0

Environment

Any compatible android version

Steps to reproduce

1. Launch AdGuard
2. Enable protection along with the DNS Protection module
3. Go to the Settings tab -> General -> Advanced -> Low-level
4. Set the Fallback upstreams to Automatic DNS
5. Disable the Validate DNS upstreams option
6. Open the Protection tab -> DNS Protection -> DNS server
7. Add and select the invalid custom dns 1.2.3.4
8. Surf some sites
9. Open the Statistics tab -> Recent activity

Expected behaviour

Queries are resolved by the fallback upstream.

Actual behaviour

Requests in the recent activity log marked as SERVFAIL. The invalid 1.2.3.4 DNS is still in use.

Additional info

This issue persists for the invalid plain dns, but the invalid encrypted dns upstream switches to the fallbacks correctly.