getCookie() function fails on a particular document.cookie string

I am talking about this piece of code

  function getCookie(name) {
    var dc = document.cookie;
    var prefix = name + "=";
    var begin = dc.indexOf("; " + prefix);
    if (begin == -1) {
      begin = dc.indexOf(prefix);
      if (begin != 0) return null;
    } else {
      begin += 2;
      var end = document.cookie.indexOf(";", begin);
      if (end == -1) end = dc.length;
    }
    return decodeURI(dc.substring(begin + prefix.length, end));
  }

  if(getCookie('cookie_notice_accepted') === 'true') {

My document.cookie is "cookie_notice_accepted=true; DO-LB=node-196037985|XvH1v|Xv". the DO-LB cookie is a load balancer cookie which is set using the Set-Cookie HTTP header on each request, on Chrome it is at the end of the string.

However, when getCookie('cookie_notice_accepted') is called, it returns "true; DO-LB=node-196037985|XvH1v|Xv" when in reality it should return just "true".

Please fix this soon, we have a production website with this issue.