Fixed Don't autolink invalid URLs like "http://"

[Steffen]

Affected version

2.0.7

If a user enters the following text (they are talking about IPv6 addresses):

What about (http://[<ipv6-address>])?

Then XenForo autolinks it like this:

What about ([URL]http://[/URL][<ipv6-address>])?

Obviously, http:// is not a valid URL.

Maybe XenForo could call filter_var($url, FILTER_VALIDATE_URL) to check whether the maybe-URL it is about to autolink is valid?