conf_regen: Fix mdns

hooks/conf_regen/37-mdns

@@ -24,10 +24,10 @@ set -Eeuo pipefail
 _generate_config() {
     echo "domains:"
     # Add yunohost.local (only if yunohost.local ain't already in ynh_domains)
-    if ! echo "$YNH_DOMAINS" | tr ' ' '\n' | grep -q --line-regexp 'yunohost.local'; then
+    if ! echo "${YNH_DOMAINS:-}" | tr ' ' '\n' | grep -q --line-regexp 'yunohost.local'; then
         echo "    - yunohost.local"
     fi
-    for domain in $YNH_DOMAINS; do
+    for domain in ${YNH_DOMAINS:-}; do
         # Only keep .local domains (don't keep
         [[ "$domain" =~ [^.]+\.[^.]+\.local$ ]] && echo "Subdomain $domain cannot be handled by Bonjour/Zeroconf/mDNS" >&2
         [[ "$domain" =~ ^[^.]+\.local$ ]] || continue