Fixed a bug where a notification could get removed

If the following calls were made, the second notification
would disappear even though it should still be around:

1: addNotification(key) (HUN)
2: cancelNotification(key) (<2s after 1.)
3: addNotification(key)

This is now fixed.

Change-Id: Ibe108d60ca92ed076e4f44694a76904fabeee970