prettyDiskSize should return something descriptive instead of NaN

undefined

src/js/index.js

@@ -274,6 +274,7 @@ app.filter('prettyMemory', function () {
 
 app.filter('prettyDiskSize', function () {
     return function (size) {
+        if (!size) return 'not available yet';
         var i = Math.floor(Math.log(size) / Math.log(1024));
         return (size / Math.pow(1024, i)).toFixed(2) * 1 + ' ' + ['B', 'kB', 'MB', 'GB', 'TB'][i]; };
 });