Don't call killTimer() on dead timers.

Change-Id: I3d8b44534d748c820ae63c6909b4eb28ff566283
Reviewed-by: Niels Weber <niels.2.weber@nokia.com>
Reviewed-by: Eike Ziller <eike.ziller@nokia.com>

src/plugins/updateinfo/updateinfoplugin.cpp

@@ -110,6 +110,7 @@ void UpdateInfoPlugin::startCheckTimer(uint milliseconds)
 void UpdateInfoPlugin::stopCurrentCheckTimer()
 {
     killTimer(d->currentTimerId);
+    d->currentTimerId = 0;
 }