Fix fdo#45779 - accessing empty polygon.

Guard access to first polygon point.

basegfx/source/tools/unotools.cxx

@@ -187,6 +187,8 @@ namespace unotools
             std::vector<awt::Point> aPoints; aPoints.reserve(nLoopCount);
             std::vector<drawing::PolygonFlags> aFlags; aFlags.reserve(nLoopCount);
 
+            if( nCount )
+            {
                 // prepare insert index and current point
                 basegfx::B2DCubicBezier aBezier;
                 aBezier.setStartPoint(rPoly.getB2DPoint(0));
@@ -252,6 +254,7 @@ namespace unotools
                     aPoints.push_back(aEnd);
                     aFlags.push_back(drawing::PolygonFlags_NORMAL);
                 }
+            }
 
             *pOuterSequence++ = comphelper::containerToSequence(aPoints);
             *pOuterFlags++ = comphelper::containerToSequence(aFlags);