desktop_printing: be a bit more defensive when launching editor
    
    Seeing a failure quite often lately where when we try and hit
    ctrl-p to print, we just type a p. There's no wait between
    maximizing and trying to print, and only a short wait on
    launch, so let's try being a bit more defensive there.
    
    Signed-off-by: Adam Williamson <awilliam@redhat.com>