avcodec/mpegvideo: Don't check for draw_horiz_band

Some parts of mpegvideo.c behave differently depending
upon whether AVCodecContext.draw_horiz_band is set or not.
This differing behaviour makes lots of FATE tests fail
and leads to garbage output, although setting this callback
is not supposed to change the output at all.

These checks have been added in commits
3994623df2 and
b68ab2609c. The commit messages
do not contain a real reason for adding the checks and it is
indeed a mystery to me. But removing these checks fixes
the FATE tests when one adds an (empty) draw_horiz_band
when using a codec that claims to support it.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

libavcodec/mpegvideo.c

@@ -1337,7 +1337,7 @@ void mpv_reconstruct_mb_internal(MpegEncContext *s, int16_t block[12][64],
         qpel_mc_func (*op_qpix)[16];
         const int linesize   = s->current_picture.f->linesize[0]; //not s->linesize as this would be wrong for field pics
         const int uvlinesize = s->current_picture.f->linesize[1];
-        const int readable = s->pict_type != AV_PICTURE_TYPE_B || IS_ENCODER(s) || s->avctx->draw_horiz_band || lowres_flag;
+        const int readable = s->pict_type != AV_PICTURE_TYPE_B || IS_ENCODER(s) || lowres_flag;
         const int block_size= lowres_flag ? 8>>s->avctx->lowres : 8;
 
         /* avoid copy if macroblock skipped in last frame too */
@@ -1584,8 +1584,6 @@ void ff_init_block_index(MpegEncContext *s){ //FIXME maybe rename
     s->dest[1] = s->current_picture.f->data[1] + (int)((s->mb_x - 1U) << (width_of_mb - s->chroma_x_shift));
     s->dest[2] = s->current_picture.f->data[2] + (int)((s->mb_x - 1U) << (width_of_mb - s->chroma_x_shift));
 
-    if(!(s->pict_type==AV_PICTURE_TYPE_B && s->avctx->draw_horiz_band && s->picture_structure==PICT_FRAME))
-    {
         if(s->picture_structure==PICT_FRAME){
         s->dest[0] += s->mb_y *   linesize << height_of_mb;
         s->dest[1] += s->mb_y * uvlinesize << (height_of_mb - s->chroma_y_shift);
@@ -1596,7 +1594,6 @@ void ff_init_block_index(MpegEncContext *s){ //FIXME maybe rename
             s->dest[2] += (s->mb_y>>1) * uvlinesize << (height_of_mb - s->chroma_y_shift);
             av_assert1((s->mb_y&1) == (s->picture_structure == PICT_BOTTOM_FIELD));
         }
-    }
 }
 
 /**