Use Nacl to decode base64 thumbnail data

www/common/common-thumbnail.js

@@ -230,20 +230,15 @@ define([
         if (!Visible.currently()) { to = window.setTimeout(interval, Thumb.UPDATE_FIRST); }
     };
 
-    var stringToBlobToUrl = function (b64) {
-        var byteString = atob(b64.split(',')[1]);
-        var ab = new ArrayBuffer(byteString.length);
-        var ia = new Uint8Array(ab);
-        for (var i = 0; i < byteString.length; i++) {
-            ia[i] = byteString.charCodeAt(i);
-        }
-        var blob = new Blob([ab], {type: "image/png"});
-        var url = URL.createObjectURL(blob);
-        return url;
-    };
+
     var addThumbnail = function (err, thumb, $span, cb) {
+        var u8 = Nacl.util.decodeBase64(thumb.split(',')[1]);
+        var blob = new Blob([u8], {
+            type: 'image/png'
+        });
+        var url = URL.createObjectURL(blob);
         var img = new Image();
-        img.src = stringToBlobToUrl(thumb);
+        img.src = url;
         $span.find('.cp-icon').hide();
         $span.prepend(img);
         cb($(img));