mpegvideo: fix forgotten lowres op_index limits

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/mpegvideo.c

@@ -2232,7 +2232,7 @@ static av_always_inline void mpeg_motion_lowres(MpegEncContext *s,
     int mx, my, src_x, src_y, uvsrc_x, uvsrc_y, uvlinesize, linesize, sx, sy,
         uvsx, uvsy;
     const int lowres     = s->avctx->lowres;
-    const int op_index   = FFMIN(lowres-1+s->chroma_x_shift, 2);
+    const int op_index   = FFMIN(lowres-1+s->chroma_x_shift, 3);
     const int block_s    = 8>>lowres;
     const int s_mask     = (2 << lowres) - 1;
     const int h_edge_pos = s->h_edge_pos >> lowres;
@@ -2356,7 +2356,7 @@ static inline void chroma_4mv_motion_lowres(MpegEncContext *s,
                                             int mx, int my)
 {
     const int lowres     = s->avctx->lowres;
-    const int op_index   = FFMIN(lowres, 2);
+    const int op_index   = FFMIN(lowres, 3);
     const int block_s    = 8 >> lowres;
     const int s_mask     = (2 << lowres) - 1;
     const int h_edge_pos = s->h_edge_pos >> lowres + 1;