SDL_WM_SetIcon behavior...

[icculus]

This might be some weird 1.2 quirk, but SDL_WM_SetIcon currently sets an existing window's icon and returns, whereas if there isn't a window it doesn't a lot of tapdancing to build a surface that it can set later...but it seems like we should probably always build that surface in case the video window goes away and then a new window is created, as the icon is singleton state in 1.2 and would apply to later windows.

(can you get rid of the SDL_SetVideoMode window without shutting down the video subsystem? Maybe that's why we do this.)