Fix shuffle always starts on first song(issues:#61) and remove redund…

[yuruxuan]

Try to fix #61

We pick a random item and put it first, instead of putting the first one first every time. And In order to make initialIndex take effect in updateQueue → _player.setAudioSource, I removed the if judgment in the replaceQueueWithItem method.

I remove _player.shuffle() when setShuffleMode(AudioServiceShuffleMode.all). It's redundant. I see the just_audio src code. When we invoke setAudioSource() method and proload is true, just_audio will call _load() method. AudioSource will be shuffled here. And platform.load() will send audioSourceMessage, initialPosition, initialIndex to native layer program.Actually audioSourceMessage contains shuffleOrder information. You can see just_audio-0.9.32/android/src/main/java/com/ryanheise/just_audio/AudioPlayer.java
at case concatenating part.

I see when I click block(or named stop) button on bottom bar. The current music always autochanged to album/playlist first item. Is this this app feature, or a bug?

Future<Duration?> _load(AudioPlayerPlatform platform, AudioSource source,
      {_InitialSeekValues? initialSeekValues}) async {

   ...

    try {
      await source._setup(this);
      checkInterruption();
      source._shuffle(initialIndex: initialSeekValues?.index ?? 0);
      _broadcastSequence();
      _durationFuture = platform
          .load(LoadRequest(
            audioSourceMessage: source._toMessage(),
            initialPosition: initialSeekValues?.position,
            initialIndex: initialSeekValues?.index,
          ))
          .then((response) => response.duration);
      
   ...

[jmshrv]

This looks like a good fix! Just tested it and it didn't have the issue that I had where it would cut off half of the album (by skipping into it).

I see when I click block(or named stop) button on bottom bar. The current music always autochanged to album/playlist first item. Is this this app feature, or a bug?

This is an intended feature. It could be modified if it would make more sense here.

[yuruxuan]

All right, I'm just asking so as not to modify some normal features : )