[fix] qwant engine - prevent API locale exception on lang 'all'

Has been reported in [1], error message::

    Error
        Error: searx.exceptions.SearxEngineAPIException
        Percentage: 0
        Parameters: ('API error::locale must be a string,locale must be one of
        the following values: en_gb, en_ie, en_us, en_ca, en_in, en_my, en_au,
        en_nz, cy_gb, gd_gb, de_de, de_ch, de_at, fr_fr, br_fr, fr_be, fr_ch,
        fr_ca, fr_ad, fc_ca, ec_ca, co_fr, es_es, es_ar, es_cl, es_co, es_mx,
        es_pe, es_ad, ca_es, ca_ad, ca_fr, eu_es, eu_fr, it_it, it_ch, pt_br,
        pt_pt, pt_ad, nl_be, nl_nl, pl_pl, zh_hk, zh_cn, fi_fi, bg_bg, et_ee,
        hu_hu, da_dk, nb_no, sv_se, ko_kr, th_th, cs_cz, ro_ro, el_gr',)
        File name: searx/engines/qwant.py:114
        Function: response
        Code: raise SearxEngineAPIException('API error::' + msg)

[1] https://github.com/searxng/searxng/issues/222

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

searx/engines/qwant.py

@@ -84,14 +84,16 @@ def request(query, params):
     )
 
     # add language tag
-    if params['language'] != 'all':
+    if params['language'] == 'all':
+        params['url'] += '&locale=en_us'
+    else:
         language = match_language(
             params['language'],
             # pylint: disable=undefined-variable
             supported_languages,
             language_aliases,
         )
-        params['url'] += '&locale=' + language.replace('-', '_')
+        params['url'] += '&locale=' + language.replace('-', '_').lower()
 
     params['raise_for_httperror'] = False
     return params
@@ -144,8 +146,8 @@ def response(resp):
         mainline_items = row.get('items', [])
         for item in mainline_items:
 
-            title = item['title']
-            res_url = item['url']
+            title = item.get('title', None)
+            res_url = item.get('url', None)
 
             if mainline_type == 'web':
                 content = item['desc']