Handle problem when pulling fails

... when e.g. sitting in a German train with bad internet connection

utils/docker-nginx.tls13-earlydata.start.sh

@@ -6,6 +6,8 @@ ID=$(docker run -d -ti $image)
 
 echo $ID
 
+[[ "$ID" ]] && echo "container couldn't be retrieved" >&2 && exit 1
+
 docker exec -ti $ID nginx -V
 docker exec -ti $ID mkdir /etc/nginx/ssl
 HN=$(docker exec -ti $ID hostname| tr -d '\n' | tr -d '\r')