Fix regression introduced in 16e486e.

Explicitly select the first tab if the caller hasn't done so by the time
we're attached to the window.

src/kits/interface/TabView.cpp

@@ -569,7 +569,8 @@ BTabView::AttachedToWindow()
 {
 	BView::AttachedToWindow();
 
-	Select(fSelection);
+	if (fSelection < 0)
+		Select(0);
 }