tdf#115671 vcl opengl: fix drawing of polylines with duplicate points

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

vcl/opengl/gdiimpl.cxx

@@ -1601,7 +1601,12 @@ bool OpenGLSalGraphicsImpl::drawPolyLine(const basegfx::B2DPolygon& rPolygon, do
 {
     VCL_GL_INFO("::drawPolyLine " << rPolygon.getB2DRange());
 
-    mpRenderList->addDrawPolyLine(rPolygon, fTransparency, rLineWidth, eLineJoin, eLineCap,
+    // addDrawPolyLine() assumes that there are no duplicate points in the
+    // polygon.
+    basegfx::B2DPolygon aPolygon(rPolygon);
+    aPolygon.removeDoublePoints();
+
+    mpRenderList->addDrawPolyLine(aPolygon, fTransparency, rLineWidth, eLineJoin, eLineCap,
                                   fMiterMinimumAngle, mnLineColor, mrParent.getAntiAliasB2DDraw());
     PostBatchDraw();
     return true;