This fixes a bug that can reproduced with these steps:
* Start openttd in fullscreen mode
* Turn off fullscreen mode
* Try to resize the window. The window can't be resized.
SDL_GetVideoDriver(0) returns name of first video driver included in
the library, not the driver currently used.
SDL_GetCurrentVideoDriver() does what we want here.
This function requires libSDL 2.0.5 or higher. It looks like we don't
need to use it, and can just use the original SDL_CreateRGBSurface(),
with the masks set to 0, to trigger the default 8-bit format, which is
SDL_PIXELFORMAT_INDEX8.
Closes#7785
Note: this code path is activated by using an 8-bit blitter, like:
./bin/openttd -b 8bpp-simple
nikolas