Fixed multiple artists

Tracks with multiple artists used to cause rendering issues and crashes
because then `artist` field was a list of strings while miniplayer
incorrectly assumed it to be a single string. The issue is fixed by
compiling multiple artists into a single string, separating them with
commas.

bin/miniplayer

@@ -623,6 +623,9 @@ class Player:
         except KeyError:
             artist = ""
 
+        if type(artist) is list:
+            artist = ", ".join(artist)
+
         try:
             title = song["title"]
         except KeyError: