mpegvideo: do not set current_picture_ptr in decoders

This code was originally added in
5f1948111a to h263 to set decoded frame
pts to some random numbers (removed in
a1c5cc429d) and then cargo culted to other
decoders.

The code is left in h263dec for now, since some part of the decoder
(apparently OBMC) relies on the specific previous frame to be reused.

libavcodec/h261dec.c

@@ -584,15 +584,6 @@ retry:
         if (ff_MPV_common_init(s) < 0)
             return -1;
 
-    /* We need to set current_picture_ptr before reading the header,
-     * otherwise we cannot store anything in there. */
-    if (s->current_picture_ptr == NULL || s->current_picture_ptr->f.data[0]) {
-        int i = ff_find_unused_picture(s, 0);
-        if (i < 0)
-            return i;
-        s->current_picture_ptr = &s->picture[i];
-    }
-
     ret = h261_decode_picture_header(h);
 
     /* skip if the header was thrashed */

libavcodec/mss2.c

@@ -377,13 +377,6 @@ static int decode_wmv9(AVCodecContext *avctx, const uint8_t *buf, int buf_size,
 
     ff_mpeg_flush(avctx);
 
-    if (s->current_picture_ptr == NULL || s->current_picture_ptr->f.data[0]) {
-        int i = ff_find_unused_picture(s, 0);
-        if (i < 0)
-            return i;
-        s->current_picture_ptr = &s->picture[i];
-    }
-
     init_get_bits(&s->gb, buf, buf_size * 8);
 
     s->loop_filter = avctx->skip_loop_filter < AVDISCARD_ALL;

libavcodec/vc1dec.c

@@ -5914,15 +5914,6 @@ static int vc1_decode_frame(AVCodecContext *avctx, void *data,
         }
     }
 
-    /* We need to set current_picture_ptr before reading the header,
-     * otherwise we cannot store anything in there. */
-    if (s->current_picture_ptr == NULL || s->current_picture_ptr->f.data[0]) {
-        int i = ff_find_unused_picture(s, 0);
-        if (i < 0)
-            goto err;
-        s->current_picture_ptr = &s->picture[i];
-    }
-
     // do parse frame header
     v->pic_header_flag = 0;
     v->first_pic_header_flag = 1;