The bugdoc had a custom shape, the interesting part of it was a triangle
with miter line join, where the last segment was missing. In that case
RenderList::addDrawPolyLine() mishandled the polyline, as it does not
expect duplicate points in it.

Change-Id: I06d5c2d191bb6269a87da1f006f27a94205f5145
Reviewed-on: https://gerrit.libreoffice.org/56879Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
Tested-by: Jenkins