notification: Prevent the timer to be started early in the constructor.

Otherwise the timer will be started before the preset is applied.

lib/naughty/notification.lua

@@ -439,7 +439,11 @@ end
 function notification:reset_timeout(new_timeout)
     if self.timer then self.timer:stop() end
 
+    -- Do not set `self.timeout` to `self.timeout` since that would create the
+    -- timer before the constructor ends.
+    if new_timeout and self.timer then
         self.timeout = new_timeout or self.timeout
+    end
 
     if self.timer and not self.timer.started then
         self.timer:start()