scripting: fix array copy and, use System.arraycopy

Change-Id: If8addcc5d95f610ade404e62e4a2a775319e9ff3
Reviewed-on: https://gerrit.libreoffice.org/11354
Reviewed-by: Noel Grandin <noelgrandin@gmail.com>
Tested-by: Noel Grandin <noelgrandin@gmail.com>