[apps] Add headers in all sub tab view for a better rendering

Change-Id: Id9fc1ffac9cbc4bebc9af7daf410f36279555519

apps/graph/values/values_controller.cpp

@@ -100,6 +100,9 @@ ViewController * ValuesController::intervalParameterController() {
 }
 
 int ValuesController::numberOfButtons() const {
+  if (isEmpty()) {
+    return 0;
+  }
   return 1;
 }