workaround for #457 (#465)

i'm not in anyway versed in javascript, but this hack fixes #457 for me.

share/public/javascripts/portsort.js

@@ -30,6 +30,8 @@ function portSort (a, b) {
         // octal regex
         ore = /^0/,
         // convert all to strings and trim()
+        if (typeof a == 'null') { a = ''; }
+        if (typeof b == 'null') { b = ''; }
         x = a.toString().replace(sre, '') || '',
         y = b.toString().replace(sre, '') || '';