when we have two definitions of the same method in a straight
inheritance path up our hierarchy, we were missing a warning

Change-Id: Ibc0f11644c7321a0d5618024860c2503665d8835
Reviewed-on: https://gerrit.libreoffice.org/58354
Tested-by: Jenkins
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>