[Backport 4.0] broken sendRedirect

Reproduction path:

1. create an archetype project
2. add a custom component which redirects to the homepage, for example

   public class RedirectComponent extends CommonComponent {
       @Override
       public void doBeforeRender(final HstRequest request, final HstResponse response) {
           super.doBeforeRender(request, response);
           Map<String, String[]> queryParams = new HashMap<>();
           queryParams.put("noresults", new String[]{"true"});
           sendRedirect(request.getRequestContext().getResolvedMount().getMount().getHomePage(), request, response, queryParams);
       }
   }
   

3. configure the component class on some page and link a sitemap called redirect on it
4. browse the site on http://localhost:8080/site/redirect

The result is that the page is broken and the following warning will be logged:

[INFO] [talledLocalContainer] 04.11.2016 14:46:07 WARN  http-nio-8080-exec-1 [AggregationValve.invoke:227] Exception during sendRedirect. java.lang.IllegalStateException: Cannot call sendRedirect() after the response has been committed