Fixes #3377 - chat-no-jquery(.min).js is logging an javascript exception (Uncaught ReferenceError: node is not defined)

public/assets/chat/chat-no-jquery.coffee

@@ -931,7 +931,7 @@ do(window) ->
     onInput: =>
       # remove unread-state from messages
       for message in @el.querySelectorAll('.zammad-chat-message--unread')
-        node.classList.remove 'zammad-chat-message--unread'
+        message.classList.remove 'zammad-chat-message--unread'
 
       sessionStorage.setItem 'unfinished_message', @input.innerHTML
 

public/assets/chat/chat-no-jquery.js

@@ -1431,7 +1431,7 @@ var extend = function(child, parent) { for (var key in parent) { if (hasProp.cal
       ref = this.el.querySelectorAll('.zammad-chat-message--unread');
       for (j = 0, len = ref.length; j < len; j++) {
         message = ref[j];
-        node.classList.remove('zammad-chat-message--unread');
+        message.classList.remove('zammad-chat-message--unread');
       }
       sessionStorage.setItem('unfinished_message', this.input.innerHTML);
       return this.onTyping();