- screenshots on native wayland (SDL_VIDEODRIVER=wayland) were black,
at least on Gnome
=> fixed(?) by reading from the default (back) buffer instead of
the front buffer
- after taking a screenshot, resizing the window (or switching to
fullscreen) was broken (window remained black or became invisible
or partly contained garbage), both with native wayland and xwayland
=> fixed by restoring the glReadBuffer state after reading the pixels