AK: Fix IPv6 serialization on multiple '0' parts ending in a '0' part

This could happen if a sequence of '0' parts was followed by a longer
sequence of '0' parts at the end of the host. The first sequence was
being used for the compress, and not the second.

For example, [1:1:0:0:1:0:0:0] was being serialized as: [1:1::1:0:0:0]
instead of [1:1:0:0:1::].

Fix this by checking at the end of the loop if we are in the middle of a
sequence of '0' parts that is longer than the current longest.

Tests/LibWeb/Text/input/URL/url.html

@@ -18,6 +18,7 @@
             'ftp://serenityos.org:21',
             'http://[0:1:0:1:0:1:0:1]',
             'http://[1:0:1:0:1:0:1:0]',
+            'http://[1:1:0:0:1:0:0:0]/',
         ]) {
             printURL(url);
         }