[fix] ddg-lite vqd value: some search terms do not have a vqd value

Some search terms do not have results and therefore no vqd value

BTW: remove a leftover from 9197efa

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

searx/engines/duckduckgo.py

@@ -98,7 +98,12 @@ def get_vqd(query):
     query_url = 'https://lite.duckduckgo.com/lite/?{args}'.format(args=urlencode({'q': query}))
     res = get(query_url)
     doc = lxml.html.fromstring(res.text)
-    value = doc.xpath("//input[@name='vqd']/@value")[0]
+    value = doc.xpath("//input[@name='vqd']/@value")
+    if value:
+        value = value[0]
+    else:
+        # some search terms do not have results and therefore no vqd value
+        value = ''
     logger.debug("new vqd value: %s", value)
     cache_vqd(query, value)
     return value
@@ -236,9 +241,6 @@ def request(query, params):
         params['data']['s'] = offset
         params['data']['dc'] = offset + 1
 
-    # request needs a vqd argument
-    params['data']['vqd'] = get_vqd(query)
-
     # initial page does not have additional data in the input form
     if params['pageno'] > 1: