miscalculation of header_bits when using the -thread option bugfix, patch by (Christophe Massiot <cmassiot at freebox dot fr>)

Originally committed as revision 3329 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/mpegvideo.c

@@ -4652,7 +4652,6 @@ static void merge_context_after_encode(MpegEncContext *dst, MpegEncContext *src)
     MERGE(dct_count[0]); //note, the other dct vars are not part of the context
     MERGE(dct_count[1]);
     MERGE(mv_bits);
-    MERGE(header_bits);
     MERGE(i_tex_bits);
     MERGE(p_tex_bits);
     MERGE(i_count);