spice: flush drawing before notifying client

This solves the client having slow/outdated VGA/2D console. It's a
regression introduced when the code was switched to render it via opengl
in commit 4423184376d ("spice/gl: render DisplaySurface via opengl")

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20210216092056.2301293-2-marcandre.lureau@redhat.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
1 file changed