Zeroed out SDL_Surface::unused1 so glSDL will work on stock SDL

--HG--
extra : convert_revision : svn%3Ac70aab31-4412-0410-b14c-859654838e24/trunk%40442

src/video/SDL_surface.c

@@ -107,6 +107,7 @@ SDL_Surface * SDL_CreateRGBSurface (Uint32 flags,
 	surface->locked = 0;
 	surface->map = NULL;
 	surface->format_version = 0;
+	surface->unused1 = 0;
 	SDL_SetClipRect(surface, NULL);
 
 	/* Get the pixels */