Better handling for MXF essence reading reaching EOF.

If no metadata follows MXF essence, that is essence ends with EOF,
"Operation not permitted" error was produced and a non-zero code
was returned from ffmpeg executable.
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/mxfdec.c

@@ -2210,10 +2210,8 @@ static int mxf_read_packet_old(AVFormatContext *s, AVPacket *pkt)
     KLVPacket klv;
     MXFContext *mxf = s->priv_data;
 
-    while (!url_feof(s->pb)) {
+    while (klv_read_packet(&klv, s->pb) == 0) {
         int ret;
-        if (klv_read_packet(&klv, s->pb) < 0)
-            return -1;
         PRINT_KEY(s, "read packet", klv.key);
         av_dlog(s, "size %"PRIu64" offset %#"PRIx64"\n", klv.length, klv.offset);
         if (IS_KLV_KEY(klv.key, mxf_encrypted_triplet_key)) {
@@ -2298,7 +2296,7 @@ static int mxf_read_packet_old(AVFormatContext *s, AVPacket *pkt)
         skip:
             avio_skip(s->pb, klv.length);
     }
-    return AVERROR_EOF;
+    return url_feof(s->pb) ? AVERROR_EOF : -1;
 }
 
 static int mxf_read_packet(AVFormatContext *s, AVPacket *pkt)