avcodec/vdpau: fix render2() check

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/vdpau.c

@@ -237,7 +237,7 @@ FF_DISABLE_DEPRECATION_WARNINGS
 FF_ENABLE_DEPRECATION_WARNINGS
 #endif
 
-    if (!hwctx->render) {
+    if (!hwctx->render && hwctx->render2) {
         status = hwctx->render2(avctx, frame, (void *)&pic_ctx->info,
                                 pic_ctx->bitstream_buffers_used, pic_ctx->bitstream_buffers);
     } else