Fix encoding of IDN hostnames with QUrl::host

When the formatting parameter wasn't exactly QUrl::EncodeUnicode, it
wouldn't encode, despite having to.

Change-Id: Id75834dab9ed466e94c7ffff1444bacc08dd109b
Reviewed-by: Frederik Gladhorn <frederik.gladhorn@theqtcompany.com>
Reviewed-by: Edward Welbourne <edward.welbourne@theqtcompany.com>