There are some scenarios (e.g. WKWebView) where Bowser can't detect the
Safari version number correctly, which may lead to unexpected behavior
if any code that relies on this utils use the version number exported
unchecked.
In such cases, use the WebKit version to determine it. If that's not the
case and the version number is still unavailable, log an warning and
return Infinity so that we do not deny access to the user (even if
we're uncertain about whether it's a supported browser);
