self.js: delete invalid cookie before redirecting

frontend/js/self.js

@@ -6,8 +6,14 @@
       "ownerToken": global.cookieGet("commentoOwnerToken"),
     };
 
+    if (json.ownerToken === undefined) {
+      document.location = "/login";
+      return;
+    }
+
     global.post(global.commentoOrigin + "/api/owner/self", json, function(resp) {
       if (!resp.success || !resp.loggedIn) {
+        global.cookieDelete("commentoOwnerToken");
         document.location = "/login";
         return;
       }

frontend/js/utils.js

@@ -75,6 +75,12 @@
   }
 
 
+  // Deletes a cookie.
+  global.cookieDelete = function(name) {
+    document.cookie = name + '=;expires=Thu, 01 Jan 1970 00:00:01 GMT;';
+  }
+
+
   // Converts a date in the past to a human-friendly duration relative to now.
   global.timeSince = function(date) {
     var seconds = Math.floor((new Date() - date) / 1000);