mpeg12: Fix non-hwaccel VDPAU decode.

Previously avctx->hwaccel would have been set to a dummy value,
now an explicit check is necessary instead.

Signed-off-by: Reimar Döffinger <Reimar.Doeffinger@gmx.de>

libavcodec/mpeg12.c

@@ -1349,7 +1349,7 @@ static int mpeg_decode_postinit(AVCodecContext *avctx)
         avctx->hwaccel = ff_find_hwaccel(avctx->codec->id, avctx->pix_fmt);
         // until then pix_fmt may be changed right after codec init
         if (avctx->pix_fmt == AV_PIX_FMT_XVMC_MPEG2_IDCT ||
-            avctx->hwaccel )
+            avctx->hwaccel || uses_vdpau(avctx))
             if (avctx->idct_algo == FF_IDCT_AUTO)
                 avctx->idct_algo = FF_IDCT_SIMPLE;
 
@@ -2085,7 +2085,7 @@ static int vcr2_init_sequence(AVCodecContext *avctx)
     avctx->pix_fmt = mpeg_get_pixelformat(avctx);
     avctx->hwaccel = ff_find_hwaccel(avctx->codec->id, avctx->pix_fmt);
 
-    if( avctx->pix_fmt == AV_PIX_FMT_XVMC_MPEG2_IDCT || avctx->hwaccel )
+    if (avctx->pix_fmt == AV_PIX_FMT_XVMC_MPEG2_IDCT || avctx->hwaccel || uses_vdpau(avctx))
         if (avctx->idct_algo == FF_IDCT_AUTO)
             avctx->idct_algo = FF_IDCT_SIMPLE;