the GDI+ version make the nk_button_color draw the rectangle with inner black lines

the GDI+ fix make the nk_button_color draw the rectangle with inner black lines, while the original one is ok. I found the PR make change of the GDI+, maybe it's the reason of problem. https://github.com/vurtun/nuklear/pull/527 The GDI+ fix version The Original Version