Convert host to IDNA ASCII form

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | 
| License       | MIT
| Doc PR        | NA

`checkdnsrr()` returns `false` if the host contains unusual characters.
Converting it using `idn_to_ascii()` prevents that.