DecoderAPI: pass SignedSongTime to decoder_initialized()

src/decoder/DecoderAPI.hxx

@@ -53,12 +53,13 @@ class Error;
  * @param audio_format the audio format which is going to be sent to
  * decoder_data()
  * @param seekable true if the song is seekable
- * @param total_time the total number of seconds in this song; -1 if unknown
+ * @param duration the total duration of this song; negative if
+ * unknown
  */
 void
 decoder_initialized(Decoder &decoder,
 		    AudioFormat audio_format,
-		    bool seekable, float total_time);
+		    bool seekable, SignedSongTime duration);
 
 /**
  * Determines the pending decoder command.