awful.tooltip: ensure tooltip is attached to a screen

Signed-off-by: Sébastien Gross <seb•ɱɩɲʋʃ•awesome•ɑƬ•chezwam•ɖɵʈ•org>
Signed-off-by: Julien Danjou <julien@danjou.info>

lib/awful/tooltip.lua.in

@@ -89,10 +89,10 @@ end
 local function show(self)
     -- do nothing if the tooltip is already shown
     if self.visible then return end
-    if data[self].timer then
-        if not data[self].timer.started then
     -- make sure the tooltip is on the same screen as the mouse
     self.wibox.screen = mouse.screen
+    if data[self].timer then
+        if not data[self].timer.started then
             data[self].timer_function()
             data[self].timer:start()
         end