moved currentChunk into OutputBuffer

currentChunk is a global variable, which renders the whole output
buffer code non-reentrant.  Although this is not a real problem since
there is only one global output buffer currently, we should move it to
the OutputBuffer struct.

git-svn-id: https://svn.musicpd.org/mpd/trunk@7284 09075e82-0dd4-0310-85a5-a0d7c8717e4f

src/outputBuffer.h

@@ -52,6 +52,8 @@ typedef struct _OutputBuffer {
 	/** the index after the last decoded chunk */
 	mpd_uint16 volatile end;
 
+	mpd_sint16 currentChunk;
+
 	AudioFormat audioFormat;
 	ConvState convState;
 } OutputBuffer;