dde_kit: Allow re-scheduling from timer handler

Prior this change, the attempt to re-schedule a timer from its timer
handler resulted in a clear '_pending' flag. This caused the timer event
to disappear from the scheduling queue without the handler being called
ever again. By resetting the '_pending' value before calling the hander,
we prevent a re-scheduled '_pending' flag to be cleared immediately
after calling the handler.

os/src/lib/dde_kit/timer.cc

@@ -138,8 +138,8 @@ class dde_kit_timer : public Alarm, public List<dde_kit_timer>::Element
 		{
 			/* if timer is really pending, call registered handler function */
 			if (_pending) {
-				_handler(_priv);
 				_pending = false;
+				_handler(_priv);
 			}
 
 			/* do not schedule again */