fix error where _search_all_access() in library.py would return None if no searchable filters where passed. _search_all_access() now returns an empty search result if the search could not be performed.
fix error where _search_all_access() in library.py would return None if no searchable filters where passed. _search_all_access() now returns an empty search result if the search could not be performed.

jodal/mopidy-gmusic,mopidy/mopidy-gmusic,hechtus/mopidy-gmusic,elrosti/mopidy-gmusic