Only copy Composer auth.json if target dir exists

compose/bin/setup-composer-auth

@@ -26,6 +26,6 @@ fi
 echo "composer config --global http-basic.repo.magento.com ${PUBLIC_KEY} ${PRIVATE_KEY}" | bin/clinotty bash -
 
 # Also make sure alternate auth.json is setup (Magento uses this internally)
-bin/clinotty cp /var/www/.composer/auth.json ./var/composer_home/auth.json
+bin/clinotty [ -d "./var/composer_home" ] && cp /var/www/.composer/auth.json ./var/composer_home/auth.json
 
 echo "Composer auth has been setup."