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/expected/URL/url.txt

@@ -34,3 +34,12 @@ hostname => '[1:1:0:0:1::]'
 port => ''
 pathname => '/'
 search => ''
+unknown://serenityos.org:0
+protocol => 'unknown:'
+username => ''
+password => ''
+host => 'serenityos.org:0'
+hostname => 'serenityos.org'
+port => '0'
+pathname => ''
+search => ''

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);
         }