- crashed due to out-of-range index with empty vector
- kill pruposeless manual index fiddling for good
- add trivial test

Change-Id: Ic224c70f432d2b26718e05aa5a2742461cfb7bec
Reviewed-on: https://gerrit.libreoffice.org/16749Reviewed-by: Michael Meeks <michael.meeks@collabora.com>
Tested-by: Michael Meeks <michael.meeks@collabora.com>