Fix Tree::get_column_at_position crash

(cherry picked from commit c8efcf81d288068f9c8b5803f57f2aa4e51e959e)

scene/gui/tree.cpp

@@ -3974,6 +3974,8 @@ Tree::Tree() {
 
 	allow_reselect = false;
 	propagate_mouse_activated = false;
+
+	update_cache();
 }
 
 Tree::~Tree() {