Fix the subdomain detection, substr was using a wrong offset length

[edhelas]

Everything is in the title :)

[Vitorinox]

Example:

$host = "sub.example.com", $adapterHost = "example.com":
Original: substr("sub.example.com", -11 + 1) = "xample.com" vs .example.com → false.
Modified: substr("sub.example.com", -11 - 1) = ".example.com" vs .example.com → true.

The change fixes the subdomain check by adjusting the substring start position to include the leading dot, ensuring accurate detection of subdomains.

[oscarotero]

Thank you @edhelas for the change and @Vitorinox for the review!