lookup: Make artist lookup ignore unavailable albums

This reduces the amount of returned data a lot, since we don't include
both available albums and unavailable albums autolinked to the available
album.

This also makes artist lookup notably faster, improving from 2.27s to
0.75s for a worst-case artist.

Fixes #31

mopidy_spotify/lookup.py

@@ -71,6 +71,8 @@ def _lookup_artist(config, sp_link):
     sp_album_browsers = []
     for sp_album in sp_artist_browser.albums:
         sp_album.load()
+        if not sp_album.is_available:
+            continue
         if sp_album.type is spotify.AlbumType.COMPILATION:
             continue
         if sp_album.artist.link.uri in _VARIOUS_ARTISTS_URIS:

tests/test_lookup.py

@@ -100,6 +100,18 @@ def test_lookup_of_artist_uri(
     assert track.bitrate == 160
 
 
+def test_lookup_of_artist_ignores_unavailable_albums(
+        session_mock, sp_artist_browser_mock, sp_album_browser_mock, provider):
+    sp_artist_mock = sp_artist_browser_mock.artist
+    session_mock.get_link.return_value = sp_artist_mock.link
+    sp_album_mock = sp_album_browser_mock.album
+    sp_album_mock.is_available = False
+
+    results = provider.lookup('spotify:artist:abba')
+
+    assert len(results) == 0
+
+
 def test_lookup_of_artist_uri_ignores_compilations(
         session_mock, sp_artist_browser_mock, sp_album_browser_mock, provider):
     sp_artist_mock = sp_artist_browser_mock.artist