check if next is not defined

lms/templates/login.html

@@ -51,7 +51,11 @@
       $('#login-form').on('ajax:success', function(event, json, xhr) {
         if(json.success) {
           var u=decodeURI(window.location.search);
-          var next=decodeURIComponent(u.split("next=")[1]);
+          var next = u.split("next=")[1];
+          if (next != undefined) {
+            // if next is undefined, decodeURI returns "undefined" causing a bad redirect.
+            next = decodeURI(next); 
+	  }		
           if (next && !isExternal(next)) {
             location.href=next;
           }  else if(json.redirect_url){