notification: Set the ID earlier.

Otherwise the signals were sent and the widgets created before the ID
was set. This makes some attempt at detecting updated notifications
error prone.

lib/naughty/notification.lua

@@ -580,6 +580,8 @@ local function create(args)
 
     gtable.crush(n, notification, true)
 
+    n.id = n.id or notification._gen_next_id()
+
     -- Allow extensions to create override the preset with custom data
     naughty.emit_signal("request::preset", n, args)
 
@@ -597,8 +599,6 @@ local function create(args)
         n:set_timeout(n._private.timeout or n.preset.timeout)
     end
 
-    n.id = notification._gen_next_id()
-
     return n
 end