vc1: fix decoding when end sequence is present

Signed-off-by: Mans Rullgard <mans@mansr.com>
(cherry picked from commit fb985071)

libavcodec/vc1dec.c

@@ -3149,7 +3149,7 @@ static int vc1_decode_frame(AVCodecContext *avctx,
     const uint8_t *buf_start = buf;
 
     /* no supplementary picture */
-    if (buf_size == 0) {
+    if (buf_size == 0 || (buf_size == 4 && AV_RB32(buf) == VC1_CODE_ENDOFSEQ)) {
         /* special case for last picture */
         if (s->low_delay==0 && s->next_picture_ptr) {
             *pict= *(AVFrame*)s->next_picture_ptr;