vc1dec: Call ff_vdpau_vc1_decode_picture() once for each field.

Fixes mplayer -vc ffvc1vdpau for interlaced streams.

libavcodec/vc1dec.c

@@ -6008,7 +6008,12 @@ static int vc1_decode_frame(AVCodecContext *avctx, void *data,
 
     if ((CONFIG_VC1_VDPAU_DECODER)
         &&s->avctx->codec->capabilities&CODEC_CAP_HWACCEL_VDPAU)
+        if (v->field_mode && buf_start_second_field) {
+            ff_vdpau_vc1_decode_picture(s, buf_start, buf_start_second_field - buf_start);
+            ff_vdpau_vc1_decode_picture(s, buf_start_second_field, (buf + buf_size) - buf_start_second_field);
+        } else {
         ff_vdpau_vc1_decode_picture(s, buf_start, (buf + buf_size) - buf_start);
+        }
     else if (avctx->hwaccel) {
         if (v->field_mode && buf_start_second_field) {
             // decode first field