MusicChunk: initialize replay_gain_serial on demand

src/MusicChunk.hxx

@@ -84,7 +84,7 @@ struct MusicChunk {
 	 * changed since the last chunk.  The magic value 0 indicates
 	 * that there is no replay gain info available.
 	 */
-	unsigned replay_gain_serial = 0;
+	unsigned replay_gain_serial;
 
 	/** the data (probably PCM) */
 	uint8_t data[CHUNK_SIZE];

src/player/Thread.cxx

@@ -561,6 +561,7 @@ Player::SendSilence()
 	chunk->bit_rate = 0;
 	chunk->time = SignedSongTime::Negative(); /* undefined time stamp */
 	chunk->length = num_frames * frame_size;
+	chunk->replay_gain_serial = 0;
 	PcmSilence({chunk->data, chunk->length}, play_audio_format.format);
 
 	try {