javaunohelper: String comparison

Change-Id: I52a7e456bef73824f64213c982052c61e54f7c76
Reviewed-on: https://gerrit.libreoffice.org/10621
Reviewed-by: Noel Grandin <noelgrandin@gmail.com>
Tested-by: Noel Grandin <noelgrandin@gmail.com>