samples: repair viz tutorial

samples/cpp/tutorial_code/viz/creating_widgets.cpp

@@ -4,6 +4,14 @@
  * @author Ozan Cagri Tonkal
  */
 
+#ifndef USE_VTK
+#include <iostream>
+int main()
+{
+    std::cout << "This sample requires direct compilation with VTK. Stop" << std::endl;
+    return 0;
+}
+#else
 #include <opencv2/viz.hpp>
 #include <opencv2/viz/widget_accessor.hpp>
 #include <iostream>
@@ -111,3 +119,4 @@ int main()
 
     return 0;
 }
+#endif