fix bug in b2dpolypolygon::testTrapezoidHelper

ever since
    commit 82b56544
    Date:   Wed Jan 1 10:29:40 2014 +0000
    basegfx: accelerate Trapezoid subdivision by avoiding allocations.

found by my new unusedvariablemore plugin

Change-Id: Ie02f4cf576094fb1cd814efed452ae0985814065
Reviewed-on: https://gerrit.libreoffice.org/52386Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>

basegfx/test/basegfx2d.cxx

@@ -692,6 +692,7 @@ public:
         {
             B2DPoint aPoint(aPolygon.getB2DPoint(i));
             aPoint += B2DPoint(0.5-getRandomOrdinal(1),0.5-getRandomOrdinal(1));
+            aPolygonOffset.append(aPoint);
         }
         B2DPolyPolygon aPolyPolygon;
         aPolyPolygon.append(aPolygon);