[upd] wikipedia engine: return an empty result on query with illegal characters

on some queries (like an IT error message), wikipedia returns an HTTP error 400.
this commit returns an empty result instead of showing an error to the user.

searx/engines/wikipedia.py

@@ -56,6 +56,17 @@ def request(query, params):
 def response(resp):
     if resp.status_code == 404:
         return []
+
+    if resp.status_code == 400:
+        try:
+            api_result = loads(resp.text)
+        except:
+            pass
+        else:
+            if api_result['type'] == 'https://mediawiki.org/wiki/HyperSwitch/errors/bad_request' \
+               and api_result['detail'] == 'title-invalid-characters':
+                return []
+
     raise_for_httperror(resp)
 
     results = []