x11_xft resize issue

[Lory171]

Using the X11 backend with XFT fonts from demo/x11_xft, when you resize the window the font disappear. This happen because we are creating a new drawable surface for the resized window, but we are not updating the reference in XftDraw * ftdraw.

Adding the following code to the end of function nk_xsurf_resize in nuklear_xlib.h fix the issue.
#ifdef NK_XLIB_USE_XFT
XftDrawChange(surf->ftdraw, surf->drawable);
#endif
return;

[dumblob]

Yeah, just make a pull and I'll happily merge it 😉.

[Lory171]

#871