[fix] engine duden - don't raise exception on empty result list

Duden expects a word in German, so with query "amazing" the site finds nothing
and respons a 404:

    httpx.HTTPStatusError: Client error '404 Not Found' for url\
      'https://www.duden.de/suchen/dudenonline/amazing'

[1] searxng#1543 (comment)

Suggested-by: @allendema [1]
Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

searx/engines/duden.py

@@ -47,6 +47,7 @@ def request(query, params):
     # after the last page of results, spelling corrections are returned after a HTTP redirect
     # whatever the page number is
     params['soft_max_redirects'] = 1
+    params['raise_for_httperror'] = False
     return params