I found SDL_GetWindowFromID() sometimes return NULL when I start qemu via
ssh forwarding even the window has been crated already. I am not sure
whether this is a bug of SDL, but we'd better check it carefully.

Signed-off-by: Changbin Du <changbin.du@gmail.com>
Message-id: 20200427132412.17909-1-changbin.du@gmail.com
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>