Transition <rect> (without rx and ry) and <poygon> to appropriate GDI calls to fix gaps

The starts and ends of rects and polygons is the same x,y coordinate, but when the stroke is made big enough a gap will appear. The gap can be reduced (or perhaps eliminated) by setting the stroke-linecap to 'square', but it seems better (and more proper) to tell GDI they're a closed shape by using the Rectangle(...) and Polygon(...) function.