[apps] Don't forget to call viewWillAppear

At the moment ViewController::viewWillAppear doesn't do anything, so
there is no real impact. But if we want to use it it needs to be called
from subclasses.

apps/probability/distribution_controller.cpp

@@ -72,6 +72,7 @@ DistributionController::DistributionController(Responder * parentResponder, Dist
 }
 
 void Probability::DistributionController::viewWillAppear() {
+  ViewController::viewWillAppear();
   selectRow((int)m_distribution->type());
 }