Remove ipv6 entries if they're not available

src/freedombone-app-pihole

         write_config_param "PIHOLE_IFACE" "$PIHOLE_IFACE"
     fi
 
-    IPv4_address=$(get_ipv4_address)
-    IPv6_address=$(get_ipv6_address)
+    IPv4_address="$(get_ipv4_address)"
+    IPv6_address="$(get_ipv6_address)"
 
     setupVars=$piholeDir/setupVars.conf
     echo "piholeInterface=${PIHOLE_IFACE}" > ${setupVars}
     sed -i "s|@DNS2@|${PIHOLE_DNS2}|g" /etc/dnsmasq.d/01-pihole.conf
     sed -i "s|interface=.*|interface=${PIHOLE_IFACE}|g" /etc/dnsmasq.d/01-pihole.conf
     sed -i "s|@IPv4@|${IPv4_address}|g" /etc/dnsmasq.d/01-pihole.conf
-    sed -i "s|@IPv6@|${IPv6_address}|g" /etc/dnsmasq.d/01-pihole.conf
+    if [ ${#IPv6_address} -gt 0 ]; then
+        sed -i "s|@IPv6@|${IPv6_address}|g" /etc/dnsmasq.d/01-pihole.conf
+    else
+        sed -i '/@IPv6@/d' /etc/dnsmasq.d/01-pihole.conf
+    fi
     sed -i "s|@HOSTNAME@|$HOSTNAME|g" /etc/dnsmasq.d/01-pihole.conf
 
     systemctl restart dnsmasq