java: reduce excessive code indentation levels

by using early return in some methods

Change-Id: I3611c8c89b3a94ef7e1772d178acf065fd7fcdc7
Reviewed-on: https://gerrit.libreoffice.org/12374
Reviewed-by: Noel Grandin <noelgrandin@gmail.com>
Tested-by: Noel Grandin <noelgrandin@gmail.com>