MusicPipe: add MusicBuffer reference

This tiny amount of overhead allows omitting the MusicBuffer in
Clear().

src/decoder/Bridge.cxx

@@ -98,7 +98,7 @@ DecoderBridge::GetChunk() noexcept
 		return current_chunk;
 
 	do {
-		current_chunk = dc.buffer->Allocate();
+		current_chunk = dc.pipe->GetBuffer().Allocate();
 		if (current_chunk != nullptr) {
 			current_chunk->replay_gain_serial = replay_gain_serial;
 			if (replay_gain_serial != 0)
@@ -123,7 +123,7 @@ DecoderBridge::FlushChunk()
 
 	auto *chunk = std::exchange(current_chunk, nullptr);
 	if (chunk->IsEmpty())
-		dc.buffer->Return(chunk);
+		dc.pipe->GetBuffer().Return(chunk);
 	else
 		dc.pipe->Push(chunk);
 
@@ -303,11 +303,11 @@ DecoderBridge::CommandFinished()
 		/* delete frames from the old song position */
 
 		if (current_chunk != nullptr) {
-			dc.buffer->Return(current_chunk);
+			dc.pipe->GetBuffer().Return(current_chunk);
 			current_chunk = nullptr;
 		}
 
-		dc.pipe->Clear(*dc.buffer);
+		dc.pipe->Clear();
 
 		if (convert != nullptr)
 			convert->Reset();

src/decoder/DecoderControl.cxx

@@ -92,7 +92,7 @@ DecoderControl::IsCurrentSong(const DetachedSong &_song) const noexcept
 void
 DecoderControl::Start(std::unique_ptr<DetachedSong> _song,
 		      SongTime _start_time, SongTime _end_time,
-		      MusicBuffer &_buffer, MusicPipe &_pipe) noexcept
+		      MusicPipe &_pipe) noexcept
 {
 	assert(_song != nullptr);
 	assert(_pipe.IsEmpty());
@@ -100,7 +100,6 @@ DecoderControl::Start(std::unique_ptr<DetachedSong> _song,
 	song = std::move(_song);
 	start_time = _start_time;
 	end_time = _end_time;
-	buffer = &_buffer;
 	pipe = &_pipe;
 
 	ClearError();

src/decoder/DecoderControl.hxx

@@ -44,7 +44,6 @@
 #endif
 
 class DetachedSong;
-class MusicBuffer;
 class MusicPipe;
 
 enum class DecoderState : uint8_t {
@@ -152,9 +151,6 @@ struct DecoderControl final : InputStreamHandler {
 
 	SignedSongTime total_time;
 
-	/** the #MusicChunk allocator */
-	MusicBuffer *buffer;
-
 	/**
 	 * The destination pipe for decoded chunks.  The caller thread
 	 * owns this object, and is responsible for freeing it.
@@ -383,7 +379,7 @@ public:
 	 */
 	void Start(std::unique_ptr<DetachedSong> song,
 		   SongTime start_time, SongTime end_time,
-		   MusicBuffer &buffer, MusicPipe &pipe) noexcept;
+		   MusicPipe &pipe) noexcept;
 
 	/**
 	 * Caller must lock the object.

src/decoder/DecoderThread.cxx

@@ -551,7 +551,7 @@ DecoderControl::RunThread() noexcept
 			/* we need to clear the pipe here; usually the
 			   PlayerThread is responsible, but it is not
 			   aware that the decoder has finished */
-			pipe->Clear(*buffer);
+			pipe->Clear();
 
 			decoder_run(*this);
 			break;