mp3demux: pass on error code on packet read.

Reported-by: Tanami, Ohad
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
(cherry picked from commit c83442b057)

libavformat/mp3dec.c

@@ -173,7 +173,9 @@ static int mp3_read_packet(AVFormatContext *s, AVPacket *pkt)
 
     pkt->stream_index = 0;
     if (ret <= 0) {
-        return AVERROR(EIO);
+        if(ret<0)
+            return ret;
+        return AVERROR_EOF;
     }
 
     if (ret > ID3v1_TAG_SIZE &&