avcodec/cuvid: Check for non 420 chroma formats - they aren't supported

Despite the video parser seeming to correctly handle 422 and 444
chroma formats, the video decoder fails miserably to actually
decode frames - even though no errors are ever returned; you just
get frames showing unintialized garbage.
Signed-off-by: Philip Langdale <philipl@overt.org>
Signed-off-by: Timo Rothenpieler <timo@rothenpieler.org>

libavcodec/cuvid.c

@@ -137,6 +137,12 @@ static int CUDAAPI cuvid_handle_video_sequence(void *opaque, CUVIDEOFORMAT* form
         return 0;
     }
 
+    if (format->chroma_format != cudaVideoChromaFormat_420) {
+        av_log(avctx, AV_LOG_ERROR, "Chroma formats other than 420 are not supported\n");
+        ctx->internal_error = AVERROR(EINVAL);
+        return 0;
+    }
+
     avctx->coded_width = format->coded_width;
     avctx->coded_height = format->coded_height;