Fix ctkColorDialogTest2 time out

ctkColorDialog::getColor() already pops up the dialog, there is no need to
exec the app. It would otherwise hang there as no window is shown.

Libs/Widgets/Testing/Cpp/ctkColorDialogTest2.cpp

@@ -53,5 +53,5 @@ int ctkColorDialogTest2(int argc, char * argv [] )
               << std::endl;
     return EXIT_FAILURE;
     }
-  return app.exec();
+  return EXIT_SUCCESS;
 }