Mac: loading screen is black during vid_restart

[slipher]

On MacOS when in fullscreen mode, the loading screen is not rendered during a vid_restart. Also it appears to be not in fullscreen mode: what you see is a window with all black contents. Once loading finishes you re-enter fullscreen.

This is an SDL3 regression.

[slipher]

Now that #1827 is merged, this should only affect the first time the screen is drawn, where the progress is 0%.