vd_lavc: cuda requires setting hw_device_ctx

This restores cuda/cuvid under Windows.

Cuvid is relatively useless under Windows, but this was requested.

video/decode/vd_lavc.c

@@ -593,7 +593,7 @@ static void init_avctx(struct dec_video *vd, const char *decoder,
             if (ctx->hwdec_dev->restore_device)
                 ctx->hwdec_dev->restore_device(ctx->hwdec_dev);
             if (!ctx->hwdec->set_hwframes) {
-#if HAVE_VDPAU_HWACCEL
+#if HAVE_VDPAU_HWACCEL || HAVE_CUDA_HWACCEL
                 avctx->hw_device_ctx = av_buffer_ref(ctx->hwdec_dev->av_device_ref);
 #else
                 goto error;

waftools/fragments/cuda.c

@@ -2,11 +2,14 @@
 
 typedef void * CUcontext;
 
+#include <libavcodec/avcodec.h>
 #include <libavutil/hwcontext.h>
 #include <libavutil/hwcontext_cuda.h>
 
 int main(int argc, char *argv[]) {
     enum AVHWDeviceType type = AV_HWDEVICE_TYPE_CUDA;
     AVCUDADeviceContextInternal *foo;
+    AVCodecContext *avctx = avcodec_alloc_context3(NULL);
+    avctx->hw_device_ctx = NULL;
     return 0;
 }