[fix] openstreetmap engine: optmizer SPARQL query

add
hint:Query hint:optimizer "None".
to the SPARQL query to keep the response time small.

It tells the optimizer to follow the path from ?item to the different property values
instead of the other way around.
See https://www.wikidata.org/wiki/Wikidata:SPARQL_query_service/query_optimization#Property_paths

searx/engines/openstreetmap.py

@@ -42,6 +42,7 @@ route_re = re.compile('(?:from )?(.+) to (.+)')
 wikidata_image_sparql = """
 select ?item ?itemLabel ?image ?sign ?symbol ?website ?wikipediaName
 where {
+  hint:Query hint:optimizer "None".
   values ?item { %WIKIDATA_IDS% }
   OPTIONAL { ?item wdt:P18|wdt:P8517|wdt:P4291|wdt:P5252|wdt:P3451|wdt:P4640|wdt:P5775|wdt:P2716|wdt:P1801|wdt:P4896 ?image }
   OPTIONAL { ?item wdt:P1766|wdt:P8505|wdt:P8667 ?sign }