hotfix 'undefined/' bug

www/common/cryptpad-common.js

@@ -242,6 +242,11 @@ define([
     var getUserHash = common.getUserHash = function () {
         var hash = localStorage[userHashKey];
 
+        if (['undefined', 'undefined/'].indexOf(hash) !== -1) {
+            localStorage.removeItem(userHashKey);
+            return;
+        }
+
         if (hash) {
             var sHash = common.serializeHash(hash);
             if (sHash !== hash) { localStorage[userHashKey] = sHash; }