fix rip body sid when muxing cbr

Originally committed as revision 17414 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/mxfenc.c

@@ -1722,7 +1722,10 @@ static void mxf_write_random_index_pack(AVFormatContext *s)
     put_buffer(pb, random_index_pack_key, 16);
     klv_encode_ber_length(pb, 28 + 12*mxf->body_partitions_count);
 
-    put_be32(pb, 0); // BodySID of header partition
+    if (mxf->edit_unit_byte_count)
+        put_be32(pb, 1); // BodySID of header partition
+    else
+        put_be32(pb, 0); // BodySID of header partition
     put_be64(pb, 0); // offset of header partition
 
     for (i = 0; i < mxf->body_partitions_count; i++) {