~/.config/awesome/rc.lua: Prevent a nil slipping in.

That makes nasty error messages that appear when focusing an unnamed
window go away. Happy! :)

.config/awesome/rc.lua

@@ -382,5 +382,8 @@ screen[1]:connect_signal("tag::history::update", function()
end)
client.connect_signal("focus", function(c)
	if (c.name == nil) then
		return
	end
	os.execute("/home/lu/.bin/events focus '" .. c.name .. "'")
end)