Skip song if voice_client is None

src/bot.py

@@ -60,6 +60,13 @@ class Music(commands.Cog):
       try:
         await self._queue_lock.acquire()
         ctx, song = await self._queue.get()
+        if ctx.voice_client is None:
+          # Bot is no longer in a voice channel.
+          # This could be the case because a stop command was issued.
+          # We will skip this (and possibly all remaining songs) in the queue
+          self._queue.task_done()
+          self._queue_lock.release()
+          continue
         audio = discord.FFmpegPCMAudio(song.audio_url, **self._ffmpeg_options)
 
         def after(err):