[TreeTableView] set show root is applied only on click, not immediately

Run the app.
Expand the root.
Press the button to setShowRoot(false);
You can see, that this doesn't affect (I see it).
click the control to hide the root (to make button affect).

Affected tests:
ControlsAutomatedTestSuite/javafx/scene/control/test/treetable/TreeTableAsTreeTest/testTextAlignmentAfterHidingRoot