Fix grid demo stars drawing to use correct colours and font

Just add a call to SetTextColoursAndFont() now that it is present in
this renderer base class (see the parent commit) to ensure that the
correct, i.e. corresponding to the column attribute, colour is used for
the stars.

samples/grid/griddemo.cpp

@@ -162,6 +162,8 @@ public:
     {
         wxGridCellRenderer::Draw(grid, attr, dc, rect, row, col, isSelected);
 
+        SetTextColoursAndFont(grid, attr, dc, isSelected);
+
         grid.DrawTextRectangle(dc, GetStarString(GetStarValue(grid, row, col)),
                                rect, attr);
     }