Add new condition for when not removing any backups

Add a check for when retention equals 0. When retentions is set to 0 but no backups exist the message would still say "No old backups to remove for $vm".

This change changes the message as no backups would be removed even if they were found.

lxc-backup.sh

@@ -52,7 +52,7 @@ Options:
   -d  Directory where backups will be stored (default: current directory)
   -t  Manager type: lxc or incus (default: lxc)
   -x  Compression algorithm (e.g. gzip, zstd, none)
-  -c  Cleanup old backups keeping a set number (default: 2)
+  -c  Cleanup old backups and keep last <n> (default: keep all)
   -h  Show this message
 EOF
   exit 1
@@ -90,6 +90,8 @@ prune_backups() {
   if [[ ${#backup_files[@]} -gt 0 ]]; then
     echo "Removing ${#backup_files[@]} old backup files for $vm (keeping last $retention files)"
     printf '%s\0' "${backup_files[@]}" | xargs -0 rm -fv > /dev/null
+  elif [[ "${retention}" -eq 0 ]]; then
+    echo "Keeping all existing backups for $vm"
   else
     echo "No old backups to remove for $vm"
   fi