audio: Check that artwork has a default path

Instead of checking the path itself. I found that the test fails if
Emmental is installed, since it's finding the artwork in
/usr/share/icons before our local path.

Signed-off-by: Anna Schumaker <Anna@NoWheyCreamery.com>

audio/test_artwork.py

@@ -24,4 +24,4 @@ class TestAudioArtwork(unittest.TestCase):
         self.assertEqual(art.get_margin_top(), 5)
         self.assertEqual(art.get_margin_bottom(), 5)
 
-        self.assertEqual(art.get_default_path(), str(Path.absolute()))
+        self.assertIsNotNone(art.get_default_path())