display-width returns wrong value; likely window width

[jsparkes]

I'm trying to determine if I'm on a 4K monitor to set my font size larger.

(lem-sdl2/display:display-width (lem-sdl2/display:current-display)) returns 1400 no matter the monitor resolution. So does (lem-sdl2/display::display-window-width (lem-sdl2/display:current-display)) so I suspect they are calling the same SDL2 function. I peeked at the SDL2 code and it looked okay to me, so maybe the problems lies in the underlying library. Or perhaps a different surface needs to be used.