avcodec/mpegvideo: Deallocate last/next picture earlier

Fixes regression with mplayers direct rendering and reduces buffer count
pressure in some cases

Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/mpegvideo.c

@@ -1216,6 +1216,8 @@ int ff_mpv_frame_start(MpegEncContext *s, AVCodecContext *avctx)
     }
 
     ff_mpeg_unref_picture(s->avctx, &s->current_picture);
+    ff_mpeg_unref_picture(s->avctx, &s->last_picture);
+    ff_mpeg_unref_picture(s->avctx, &s->next_picture);
 
     /* release non reference frames */
     for (i = 0; i < MAX_PICTURE_COUNT; i++) {
@@ -1367,14 +1369,12 @@ int ff_mpv_frame_start(MpegEncContext *s, AVCodecContext *avctx)
     memset(s->next_picture.f->data, 0, sizeof(s->next_picture.f->data));
 #endif
     if (s->last_picture_ptr) {
-        ff_mpeg_unref_picture(s->avctx, &s->last_picture);
         if (s->last_picture_ptr->f->buf[0] &&
             (ret = ff_mpeg_ref_picture(s->avctx, &s->last_picture,
                                        s->last_picture_ptr)) < 0)
             return ret;
     }
     if (s->next_picture_ptr) {
-        ff_mpeg_unref_picture(s->avctx, &s->next_picture);
         if (s->next_picture_ptr->f->buf[0] &&
             (ret = ff_mpeg_ref_picture(s->avctx, &s->next_picture,
                                        s->next_picture_ptr)) < 0)