backends: X11: Flush connection when window was closed.
backends: X11: Flush connection when window was closed.

If one of the windows was closed the connection needs
to be flushed so that it's removed from the screen immediately.

Signed-off-by: Cyril Hrubis <b1e90efd3b808b8e0bcf2a9a55fd8b9a779bfd81@ucw.cz>

gfxprim/gfxprim,gfxprim/gfxprim,gfxprim/gfxprim,gfxprim/gfxprim,gfxprim/gfxprim