Fix release image entrypoint.sh

ci/release-image/entrypoint.sh

@@ -5,7 +5,7 @@ set -eu
 USER="$(whoami)"
 export USER
 
-if [ "${DOCKER_USER-}" != "$USER" ]; then
+if [ "${DOCKER_USER-}" ] && [ "$DOCKER_USER" != "$USER" ]; then
   echo "$DOCKER_USER ALL=(ALL) NOPASSWD:ALL" | sudo tee -a /etc/sudoers.d/nopasswd > /dev/null
   # Unfortunately we cannot change $HOME as we cannot move any bind mounts
   # nor can we bind mount $HOME into a new home as that requires a privileged container.