AK: Do not consider port of 0 as a null port

This fixes an issue where if a port number of 0 was given for a non
special scheme the port number was being dropped.

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

@@ -19,6 +19,7 @@
             '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]/',
+            'unknown://serenityos.org:0',
         ]) {
             printURL(url);
         }