ScreenSaver: ScrollToSelection off-by-one

For some reason calling PopulateScreenSaver() list in AllAttached()
scrolls the selection off-by-one, so, call PopulateScreenSaverList()
in AttachedToWindow() and then call ScrollToSelection() again in
AllAttached() which seems to fix the problem.

src/preferences/screensaver/ScreenSaverWindow.cpp

@@ -583,6 +583,8 @@ ModulesView::DetachedFromWindow()
 void
 ModulesView::AttachedToWindow()
 {
+	PopulateScreenSaverList();
+
 	fScreenSaversListView->SetTarget(this);
 	fTestButton->SetTarget(this);
 	fAddButton->SetTarget(this);
@@ -592,7 +594,8 @@ ModulesView::AttachedToWindow()
 void
 ModulesView::AllAttached()
 {
-	PopulateScreenSaverList();
+	fScreenSaversListView->ScrollToSelection();
+		// This only works after the list view is attached
 	fScreenSaversListView->Invoke(new BMessage(kMsgSaverSelected));
 }