Fix error in determin systemd support for debian 13 and newer.

update_nextcloud.sh

@@ -301,9 +301,11 @@ IFS=$CUR_IFS
 
 # - Support systemd ?
 # -
-if [[ "X$(which systemd)" = "X" ]]; then
-   SYSTEMD_EXISTS=false
-else
+SYSTEMD_EXISTS=false
+systemd=$(which systemd)
+systemctl=$(which systemctl)
+
+if [[ -n "$systemd" ]] || [[ -n "$systemctl" ]] ; then
    SYSTEMD_EXISTS=true
 fi