subsonic: Don't crash when serialising artist with no name

If the name of an artist is not set, the serialiser will crash. Instead,
just skip such an artist when serialising a list of artists.

Also add test for serialising an artist with an empty name.

Signed-off-by: Toke Høiland-Jørgensen <toke@toke.dk>

api/funkwhale_api/subsonic/serializers.py

@@ -24,6 +24,7 @@ class GetArtistsSerializer(serializers.Serializer):
 
         first_letter_mapping = collections.defaultdict(list)
         for artist in values:
+            if artist["name"]:
                 first_letter_mapping[artist["name"][0].upper()].append(artist)
 
         for letter, artists in sorted(first_letter_mapping.items()):

api/tests/subsonic/test_serializers.py

@@ -6,6 +6,7 @@ def test_get_artists_serializer(factories):
     artist1 = factories["music.Artist"](name="eliot")
     artist2 = factories["music.Artist"](name="Ellena")
     artist3 = factories["music.Artist"](name="Rilay")
+    artist4 = factories["music.Artist"](name="")  # Shouldn't be serialised
 
     factories["music.Album"].create_batch(size=3, artist=artist1)
     factories["music.Album"].create_batch(size=2, artist=artist2)
@@ -28,7 +29,7 @@ def test_get_artists_serializer(factories):
     }
 
     queryset = artist1.__class__.objects.filter(
-        pk__in=[artist1.pk, artist2.pk, artist3.pk]
+        pk__in=[artist1.pk, artist2.pk, artist3.pk, artist4.pk]
     )
 
     assert serializers.GetArtistsSerializer(queryset).data == expected