TabView: fix dynamic tab handling

Task-number: QTBUG-33162
Change-Id: I873b37bd157230f80237fd40f3e5149fbd0207ca
Reviewed-by: Volker Krause <volker.krause@kdab.com>
Reviewed-by: Jens Bache-Wiig <jens.bache-wiig@digia.com>