Fix crash when minimising while fullscreen on windows
Fix crash when minimising while fullscreen on windows

SDL behaviour looks to have changed when calling `SDL_GetWindowSize`
while minimised from a fullscreen state. This fixes crashes due to
div-by-zero propagating into the draw hierarchy.

Haven't investigated in detail why this happened, but the fix seems
solid enough to get out as a hotfix.

ppy/osu-framework,ppy/osu-framework,peppy/osu-framework,ppy/osu-framework,peppy/osu-framework,peppy/osu-framework