Comment 2 for bug 1622577

What I'm seeing here:
- the problem appears when cleanupTestCase() tries to destroy the components
- cleanupTestCase() destroys Tabs
- TabBar is somehow destroyed before its style.
- tabsModel in TabBarStyle becomes null because styledItem becomes null
- isVisible() in TabBarStyle tries to access tabsModel.count and that triggers the error.

Adding
"if (!tabsModel) return false"
is enough to fix the test, although I'm not sure that's the way we want to go. We should investigate why that wasn't needed before Qt5.6 and why, for instance, the "selected" property binding (which still relies on tabsModel.count) does not fire any error.