Clean timer in virObjectEventStateFlush

Clean timer in virObjectEventStateFlush

If the last event callback is unregistered while the event loop is
dispatching, it is only marked as deleted, but not removed.  The number
of callbacks is more than zero in that case, so the timer is not
removed.  Because it can be removed in this function now (but also
accessed afterwards so that we set 'isDispatching = false' and have it
locked), we need to temporarily increase the reference counter of the
state for the duration of this function.

Signed-off-by: Martin Kletzander <mkletzan@redhat.com>