Fix for janeczku#2547 (None isn't iterable, so in case scholary reque…

…st fails, empty list has to be returned)

cps/metadata_provider/scholar.py

@@ -54,7 +54,7 @@ def search(
                 scholar_gen = itertools.islice(scholarly.search_pubs(query), 10)
             except Exception as e:
                 log.warning(e)
-                return None
+                return list()
             for result in scholar_gen:
                 match = self._parse_search_result(
                     result=result, generic_cover="", locale=locale