Fix crash on exit. This resolves bug report 1586.

src/autostart.cpp

@@ -102,7 +102,10 @@ void updateService() {
   if (bisDesktop) service = new KService( fileName.path() );
   }
   ~desktop() {
-    delete service;
+    if(service) {
+      service = NULL;
+      delete service;
+    }
   }
 };